Polyimide vs Kapton Tube: What’s the Difference?

Kapton and polyimide are not the same thing, but every Kapton tube is a polyimide tube. Kapton is DuPont’s registered brand of polyimide film, so a “Kapton tube” is a film-based polyimide tube with a confirmed film source. The generic term “polyimide tube” also covers extruded and dip-coated constructions made from PI resin or varnish, which never contain Kapton film.

Why the Confusion Exists

The confusion is a brand-name problem, not a material problem. Kapton has been used for decades as the default name for polyimide film, the way people say “Xerox” for photocopying or “Kleenex” for tissue. Engineers inherit the habit, specifications carry it forward, and before long “Kapton tube” is written on drawings where the actual requirement is “polyimide tube.”

Quick Terminology Reference

Term	What it means
PI / polyimide	The material family — a high-performance polymer used in film, resin and varnish form
Polyimide film	PI in film form; the starting material for wound tubes
Kapton	DuPont’s registered brand of polyimide film — one film source among several
PI tube / polyimide tube	Generic term covering extruded, dip-coated, flat-wound and spiral-wound tubes
Kapton tube	A film-based PI tube wound from confirmed Kapton film
Extruded / dip-coated tube	Seamless constructions formed from PI resin or varnish — contain no film

What Is Polyimide (PI)?

Polyimide (PI) is a high-performance polymer known for thermal stability, electrical insulation and mechanical toughness. It is used in film, resin and varnish form across electronics, motors, transformers and semiconductor equipment.

Commonly cited PI film reference data:

Parameter	Reference value	Basis / source
Continuous temperature	UL-rated 220–240 °C, grade-dependent	DuPont™ Kapton® datasheets (via MatWeb)
Brief peak exposure	Up to 400 °C	DuPont™ Kapton® datasheets
Low-temperature usability	Down to −269 °C	DuPont™ Kapton® datasheets
Dielectric strength (film)	Approx. 7,700 V/mil at 1 mil (0.025 mm) film; lower at greater thickness	ASTM D149 (per film grade)
Dielectric constant	Approx. 3.4 at 1 MHz (film)	Film manufacturer datasheets
Flammability	UL 94 V-0 (selected film grades)	UL 94, per grade datasheet

These are film values. Finished-tube performance is a separate question — see “Film Data Is Not Tube Data” below.

What Is Kapton?

Kapton is a DuPont brand of polyimide film. It is a starting material, not a finished tube. When a supplier sells “Kapton tube,” it should mean a tube wound from Kapton film of a confirmed grade, with traceability to that film lot.

Using the Kapton name for extruded PI tube is incorrect — extrusion forms the tube from PI resin and produces a seamless, non-wound structure that contains no film at all. The same applies to dip-coated PI tube, which is cured from PI varnish over a mandrel.

What Is a Polyimide Tube?

“Polyimide tube” is the generic product term and covers four constructions:

Construction	Structure	Seam	Typical use
Extruded PI tube	Seamless, non-wound lumen	None	Precision tubes, capillary-size IDs, coils
Dip-coated PI tube	Coating cured over a mandrel	None	Thin-wall precision, surface control
Flat-wound PI tube	Film wound with axial overlap	Axial	Compact short sleeves, small-bore fit
Spiral-wound PI tube	Film or paper with helical overlap	Helical	Larger bores, adjustable wall build

Only the two wound constructions can involve Kapton film — and even then, the name “Kapton tube” applies only when the film source and grade are confirmed.

Kapton Tube vs Polyimide Tube: Key Differences

Aspect	Kapton tube	Polyimide tube (generic)
Material identity	DuPont™ Kapton® polyimide film, branded	Any PI film, PI resin or PI varnish
Available constructions	Film-based: flat-wound or spiral-wound	Extruded, dip-coated, flat-wound, spiral-wound
Seam	Wound (axial or helical)	Seamless options exist (extruded, dip-coated)
Lumen / format	Short sleeves typical	Coil and precision formats available
Naming requirement	Film source, grade and traceability confirmed	Generic description always applies
Temperature / dielectric data	Film data as reference; tube confirmed by sample	Same rule — film data is not tube data
Typical supply format	Cut lengths, sleeve format	Cut lengths, coils, capillary sizes

Film Data Is Not Tube Data

A film datasheet describes the film. It does not describe a finished tube. Tube performance depends on wall thickness, seam structure, winding tension, curing or bonding condition and cutting method.

For example, dielectric strength of a finished tube should be evaluated on the finished wall per ASTM D149 or IEC 60243-1 — not copied from a film datasheet. When you request a test, specify the condition: wall thickness, voltage type (AC/DC), duration and temperature. A supplier that distinguishes film data from tube data is usually the one that can actually document the tube.

How to Choose: Kapton Tube or Generic PI Tube?

Your requirement	Recommended direction
Non-wound lumen, coil or capillary-size ID	Extruded PI tube (describe as PI tube)
Thin-wall precision and surface control	Dip-coated PI tube
Compact short sleeves from film	Flat-wound PI tube; “Kapton” only with film traceability
Large bore or adjustable wall build	Spiral-wound PI tube
Brand name required in engineering documents	Confirm film source + grade before calling it Kapton tube
High-temperature electrical insulation	PI family overall; confirm continuous/peak temperature and duration

How to Write It Correctly on a Drawing

The drawing should name the requirement, not the habit. Four rules cover most specification errors:

If you need the Kapton brand, write “Kapton film, grade and lot traceability required.” The brand premium only makes sense when the film identity is documented.
If you need generic PI, write “polyimide tube, [construction], ID x wall x length, tolerance priority.” No brand name required.
Never write “Kapton” for an extruded or dip-coated part — those constructions contain no film.
Specify the test method and condition (ASTM D149 or IEC 60243-1, wall thickness, AC/DC, duration, temperature) instead of copying film datasheet values into a tube spec.

Common Specification Mistakes

Writing “Kapton tube” for an extruded part. Extruded PI tube contains no film. If the drawing demands Kapton, the part is not extruded.
Copying film dielectric values onto a tube spec. Film data and tube data differ; specify the test method and condition instead.
Assuming all polyimide tubes are Kapton. Kapton is one film brand. Other PI films, resins and varnishes produce perfectly valid polyimide tubes without the Kapton name.
Paying the Kapton premium without the traceability. The brand premium buys documented film identity. If the supplier cannot provide film source and grade evidence, you are paying for a name you are not getting.

FAQ

Is Kapton the same as polyimide?

No. Kapton is a DuPont brand of polyimide film. Polyimide is the material family; Kapton is one branded film source within it.

Why is a Kapton tube also called a polyimide tube?

Because Kapton film is polyimide. A Kapton tube is a film-based polyimide tube; the generic term also covers extruded and dip-coated constructions that do not use film.

Can any polyimide tube be called a Kapton tube?

No. The Kapton name should be used only when the film source and grade are confirmed and traceable. Extruded and dip-coated PI tubes should use the generic description.

What temperature can Kapton withstand?

Kapton film is usable down to −269 °C, is UL-rated for continuous service at 220–240 °C in many grades, and tolerates brief exposure up to 400 °C. Finished-tube capability depends on wall and construction — confirm by sample.

Is Kapton tube heat shrink?

Generally no. Kapton film does not shrink like polyester heat-shrink tubing. If shrink fit is required, review Mylar/polyester heat-shrink tubing instead.

Is extruded polyimide tube made from Kapton?

Usually not. Extruded PI tube is formed from PI resin and is seamless. Kapton is a film product, so it applies to flat-wound or spiral-wound constructions.

Engineering Recommendation

Select polyimide tubing from the complete component dimensions, operating conditions, manufacturing process and acceptance criteria. Confirm the film source before using “Kapton tube” in engineering documents. Use samples to confirm fit, seam, lumen and insulation performance before volume production.

WELLELE manufactures custom polyimide tubing in all four constructions. Send your drawing or application — we review material, process and tolerances before quotation.

Send Drawing & Application

About the Author / Review

This guide was prepared by the WELLELE engineering team, a custom electrical insulation tubing manufacturer with 20 years of production experience in the insulation series. Values cited are from published material datasheets and standard test methods; finished-tube claims are confirmed by sample testing.

Sources

DuPont™ Kapton® film datasheet values (continuous temperature, peak exposure, low-temperature usability): MatWeb polymer database / DuPont literature
Dielectric strength test method: ASTM D149 (solid electrical insulating materials)
Alternative test method reference: IEC 60243-1
Flammability: UL 94
WELLELE capability data (four constructions, custom sizes): site product pages

How to Select Insulation Tubing: A Six-Step Engineering Guide

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How to Select Insulation Tubing: A Six-Step Engineering Guide

Insulation tubing should be selected from the application conditions outward, not from a familiar material name inward. Define the electrical or fluid function, continuous and peak temperature, mechanical loads, critical dimensions, manufacturing process and qualification evidence before comparing PI, Mylar, Nomex, PEEK or fluoropolymer tubing.

In this guide

Define the function
Map the operating environment
Shortlist the material family
Specify dimensions and fit
Match the manufacturing process
Plan qualification and supplier evidence

Step 1: Define What the Tubing Must Do

Start with the function that cannot fail. A tube around a magnet wire may need dielectric separation and abrasion protection. A tube around a temperature sensor may need a thin wall, close fit and thermal response. A fluid tube may be governed by chemical compatibility, pressure, permeation and connection design.

Primary function	Questions to answer	Likely critical characteristics
Electrical insulation	What voltage, waveform, clearance and applicable standard?	Wall thickness, dielectric performance, pinholes, creepage and heat ageing
Mechanical protection	What abrasion, edge contact, vibration or assembly force?	Toughness, split resistance, surface friction and bend behavior
Thermal barrier	What continuous, peak and cycling temperatures?	Material class, shrinkage, embrittlement and dimensional stability
Fluid or gas transfer	Which medium, concentration, pressure, vacuum and cleaning cycle?	Chemical compatibility, permeation, pressure derating and fittings
Assembly aid	Must the tube slide, shrink, conform or hold a fixed shape?	Coefficient of friction, recovery, stiffness and supplied form

Step 2: Map the Complete Operating Environment

Continuous temperature alone is not a sufficient selection criterion. Record peak temperature, duration, thermal cycling, humidity, fluids, cleaning chemicals, radiation or UV exposure, vibration and whether the tube is compressed or bent while hot. For electrical equipment, include voltage type, frequency, transient conditions and the insulation system in which the tube will operate.

A useful application profile separates normal operation from foreseeable upset conditions. This prevents a supplier from approving a material against an incomplete, easier duty than the finished product will see.

Step 3: Shortlist the Material Family

Use material data as a screening tool, then verify the finished tube. Polyimide tubing is often evaluated where thin walls, heat resistance and dimensional control matter. Mylar polyester and Nomex aramid paper constructions can suit electrical insulation assemblies with different combinations of dielectric, thermal and winding requirements. PEEK and fluoropolymer tubing may be shortlisted for demanding mechanical, chemical or fluid-service conditions.

Do not transfer a resin-film or sheet datasheet value directly to a finished wound, coated or extruded tube. Construction, seam, adhesive, coating, wall build and test method can change performance. See the insulation tubing material comparison for a decision-level overview.

Step 4: Specify Dimensions, Tolerance and Fit

Define two independent tube dimensions, normally ID and OD or ID and wall thickness. Add tolerance, length, straightness, ovality and measurement conditions where they affect assembly. A nominal size without tolerance does not tell the supplier whether the tube must slide freely, locate precisely or create an interference fit.

For sleeving: provide the maximum component or conductor envelope, insertion length and required clearance.
For sensors: specify the acceptable air gap, response-time concern and whether adhesive or potting is added.
For wound tubes: identify whether overlap, seam position, wall build or mandrel release matters.
For cut parts: define length tolerance, squareness, burr, debris and packaging orientation.

Step 5: Match Material to Manufacturing Process

The same material family can produce different tube behavior through extrusion, dip coating, flat winding or spiral winding. Extrusion supports continuous polymer tube geometry. Dip coating can build thin seamless constructions on a mandrel. Flat and spiral winding allow film or paper-based structures with different seam patterns and wall builds.

Process	Useful starting point	Questions for the supplier
Extrusion	Continuous thermoplastic or fluoropolymer tubing	Resin grade, tooling, concentricity, surface and continuous length
Dip coating	Thin-wall coated tubing and tight small-diameter constructions	Layer build, cure, mandrel removal, pinhole and wall variation
Flat winding	Film or paper tube with controlled overlap	Seam, adhesive, wall build, edge quality and thermal stability
Spiral winding	Longer wound tube with helical structure	Pitch, overlap, bond, roundness and cut-end integrity

Ask for a process recommendation only after sharing the critical-to-quality characteristics. A supplier cannot optimize for wall, cost, flexibility and dimensional precision if those priorities remain unstated.

Step 6: Define Qualification Evidence Before the RFQ

Tell the supplier which documents and tests are required at quotation, sample approval and production release. Possible records include a material declaration, certificate of conformity, dimensional report, lot identification or customer-specific test report. Availability must be confirmed for the quoted material and process; a raw-material certificate does not automatically certify the finished tube.

RFQ checklist

Application, equipment and failure consequence
Material preference or allowed alternatives
ID, OD, wall, length and all tolerances
Continuous, peak and cycling temperatures
Voltage/standard or fluid/pressure/vacuum conditions
Bend, abrasion, vibration and assembly method
Quantity, annual demand and target timing
Required declarations, reports and packaging
Drawing, current sample and acceptance test

Common Tubing Selection Mistakes

The most common errors are choosing only by maximum temperature, treating nominal dimensions as complete specifications, ignoring the manufacturing seam or construction, and requesting compliance after the material has already been selected. Another frequent mistake is approving a sample for fit but not testing it through the real thermal, electrical, chemical and assembly cycles.

When a part has already failed, use a structured tubing failure analysis rather than changing material at random. If inspection language is unclear, review the guide to tubing dimensions and test methods.

Frequently Asked Questions

What information is needed to select insulation tubing?

Provide the function, operating temperature, electrical or fluid conditions, mechanical loads, ID, OD, wall, tolerance, length, assembly method, quantity and qualification requirements. A drawing plus a short application description usually prevents more errors than a material name alone.

Should I specify ID and OD or ID and wall thickness?

Either pair can define the tube geometry, but include tolerances and identify which dimension controls assembly. If both ID and OD are critical, state both. Wall thickness should not be treated as an unconstrained result when dielectric or mechanical performance depends on it.

Can the supplier recommend a lower-cost material?

Yes, if the non-negotiable requirements and validation method are clear. A lower-cost alternative should be compared on function, risk, process and qualification, not just raw-material price. Requalification cost can outweigh the unit-price saving.

When should I request a prototype?

Request a prototype when fit, assembly force, bend behavior, seam position, visual quality or process interaction cannot be proven from a drawing. State whether the prototype is representative of production tooling and material, and define the tests needed for approval.

Next Step: Request an Application Review

WELLELE can review a tubing drawing and application conditions against available materials and manufacturing routes. Recommendations remain subject to confirmed material data, process capability and customer validation in the final assembly.

Send your application, dimensions and qualification requirements for review.

Tubing Technical Data and Test Methods: What Engineers Should Specify

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Tubing Technical Data and Test Methods: What Engineers Should Specify

A useful tubing test result identifies the specimen, conditioning, equipment, method, units and acceptance rule. Resin or film typical data helps screen materials, design qualification tests validate an application, and production inspection controls the supplied tube. Mixing these three evidence levels is a common source of supplier disputes.

In this guide

Three levels of data
Dimensional inspection
Performance tests
Build a test plan
FAQ

Three Levels of Tubing Evidence

Evidence level	Purpose	Typical source	Key limitation
Material typical data	Compare candidate resins, films or papers	Raw-material manufacturer TDS	Not a guaranteed finished-tube value
Design qualification	Show the selected tube can meet defined application tests	Customer, supplier or qualified laboratory	Only valid for the tested construction and conditions
Production inspection	Control dimensions, appearance and agreed lot characteristics	Supplier inspection record or CoC	Does not replace full application validation

Dimensional Inspection: Define the Method

ID, OD, wall thickness and length appear simple, but flexible thin-wall tubes can deform under contact pressure. State the gauge type, measuring force, sample conditioning, measurement positions and calculation method. For oval tube, define whether the requirement applies to maximum, minimum or average diameter.

ID: plug/pin gauges, optical methods or section measurement may produce different practical results.
OD: micrometer contact force and tube support can affect soft material readings.
Wall: direct section measurement is not always equal to half the difference between OD and ID.
Concentricity: define maximum/minimum wall or another agreed calculation.
Length and squareness: specify datum, allowable burr, angle and measurement state.

For a supplier-focused process, see dimensional inspection and measurement.

Electrical, Thermal, Mechanical and Fluid Tests

Electrical tests can include dielectric breakdown, withstand voltage, insulation resistance or other system-specific methods. Results depend on wall, electrode geometry, conditioning, voltage ramp and environment. A film test should not be presented as a tube result without an engineering justification.

Thermal evaluation may examine dimensional change, shrinkage, embrittlement, bond integrity or electrical retention after ageing. Mechanical tests can include tensile, elongation, compression, bend, abrasion, cut-end integrity or assembly force. Fluid tube evaluation may include pressure, vacuum collapse, leakage, flow, chemical exposure or permeation.

Use the recognized ASTM, IEC, ISO, UL or customer method that applies to the product and market. If a modified method is used, describe the modification. A test name without conditions is not reproducible evidence.

How to Build a Fit-for-Purpose Test Plan

Identify the failure mode the requirement is intended to prevent.
Define the tube construction, material grade and dimensions under test.
Choose a recognized method or document the custom fixture and procedure.
State conditioning, temperature, humidity and specimen quantity.
Set units, calculation, acceptance limits and rounding rules.
Separate initial qualification, periodic validation and lot-release tests.
Define record retention, lot link and change-control triggers.

What to Ask for in a Supplier Report

A credible report identifies the product, lot, drawing revision, date, instrument, calibration status, sample size, method, individual results, acceptance limit and disposition. The exact records WELLELE can provide are subject to quotation and `[CONFIRM: actual quality system and equipment]`.

For supplier approval, combine test records with material traceability, quality-system controls and a clear change-notification agreement.

Frequently Asked Questions

Can I use a raw-material datasheet as the finished tubing specification?

Use it to identify and screen the material, but specify finished-tube dimensions, construction and performance separately. Processing, wall, seams, adhesives, coating and conditioning can change the result.

Why do two laboratories measure different wall thickness?

They may use different section preparation, instrument resolution, contact force, locations or calculations. Compare methods and raw readings before concluding that either result is wrong.

How many samples should be tested?

Sample quantity should match risk, method variability, lot definition and the applicable standard or customer plan. There is no universal number for every tubing characteristic. Agree it before quotation and production.

Does a certificate of conformity include test data?

Not necessarily. A CoC usually states conformity to specified requirements; an inspection report lists measured results. Define which document and data fields are required.

Request a Drawing and Test-Requirement Review

Send the drawing, application, method, acceptance criteria and required records. WELLELE can confirm which measurements and documents are available for the proposed tube.

Submit your tubing test and documentation requirements.

PI, Mylar, Nomex, PEEK and Fluoropolymers

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Insulation Tubing Material Comparison: PI, Mylar, Nomex, PEEK and Fluoropolymers

No single insulation tubing material is best for every design. Polyimide, polyester film, aramid paper, PEEK and fluoropolymers solve different combinations of thermal, electrical, mechanical, chemical and manufacturing problems. Engineers should compare the finished tube construction and test conditions, not select from a headline temperature or dielectric value.

In this comparison

Quick comparison
Polyimide tubing
Mylar polyester tubing
Nomex aramid paper tubing
PEEK tubing
Fluoropolymer tubing
Selection framework

Quick Engineering Comparison

Material family	Typical reason to shortlist	Construction options	Selection caution
Polyimide (PI)	Thin-wall electrical insulation, heat exposure, dimensional precision	Dip-coated, extruded or wound depending on grade and supplier process	Moisture, hydrolysis, flexing and grade/process effects require review
Polyester film (Mylar-type)	Cost-effective film insulation and wound sleeving	Flat or spiral wound, sometimes heat-shrink construction	Temperature class, seam, adhesive and shrink behavior are construction-specific
Aramid paper (Nomex-type)	Electrical insulation systems needing paper-based thermal performance	Wound paper tube, laminated or composite construction	Moisture, edge durability, bond and wall build affect the tube
PEEK	Mechanical strength, wear, heat and demanding fluid/mechanical service	Primarily extruded tube and machined/converter forms	Cost, stiffness, process window and application-specific chemical data
PTFE/FEP/PVDF	Chemical resistance, electrical insulation or fluid handling	Extruded and selected formed/converting options	Each fluoropolymer differs in temperature, clarity, stiffness, joining and permeation

This table is a screening framework, not a specification. Values depend on grade, wall, process, test method and service conditions.

When to Consider Polyimide Tubing

Polyimide tubing is commonly evaluated when the assembly needs a thin insulation wall, elevated-temperature capability and controlled small dimensions. It can support sensor, motor, probe and compact electronic applications where space is limited. The exact result depends on whether the tube is dip coated, extruded or wound and on the polymer grade.

Ask how wall thickness, pinholes, concentricity, mandrel removal, cure and cut-end quality are controlled. Do not assume a polyimide film trademark or resin datasheet represents the finished tube’s dielectric or mechanical performance.

When to Consider Mylar-Type Polyester Tubing

Polyester film tubing is often used for electrical separation, bolt or fastener sleeving, wound insulation and applications where a film-based construction offers a practical cost/performance balance. Flat or spiral winding can produce different seam patterns, overlap and wall builds.

Confirm the actual polyester film grade, adhesive or bonding system, temperature class, shrink behavior, seam orientation and moisture conditions. “Mylar” is a trademark used for specific polyester films; the supplied material identity should be stated accurately.

When to Consider Nomex-Type Aramid Paper Tubing

Aramid paper tubing can be shortlisted for motors, transformers and other electrical insulation systems that use paper-based materials. It may be wound as a tube or incorporated into a laminate. The system performance depends on paper grade, density, wall build, bond, moisture conditioning and interaction with varnish or impregnation.

Request evidence for the exact construction rather than relying only on the paper supplier’s typical data. Edge fraying, seam integrity, roundness and compression behavior may be as important as the base paper.

When to Consider PEEK Tubing

PEEK is considered when mechanical strength, wear resistance, dimensional stability and heat performance are required together. It can suit demanding equipment, sensor, aerospace, automotive, electrical and fluid applications, subject to grade and validation.

PEEK is usually a higher-cost choice, so use it where its combined properties solve a real design constraint. Review stiffness, bend radius, extrusion capability, chemical medium, pressure or load, sterilization or cleaning cycle and the required regulatory evidence.

When to Consider Fluoropolymer Tubing

PTFE is often screened for chemical inertness, low friction and electrical insulation; FEP for clearer fluid paths and melt processability; and PVDF for greater stiffness and industrial fluid systems. These materials are not interchangeable.

For fluid service, include chemical concentration, temperature, pressure, vacuum, permeation sensitivity and fittings. For electrical service, include voltage, wall, abrasion, flame requirement and the applicable standard. Review the detailed PTFE, FEP and PVDF tubing comparison before selecting a grade.

A Five-Factor Selection Framework

Thermal: continuous, peak, cycling and hot-load conditions.
Electrical or fluid: voltage system and test standard, or medium, pressure and permeation.
Mechanical: stiffness, flexibility, abrasion, vibration, compression and bend radius.
Geometry and process: ID, OD, wall, tolerance, seam, supplied length and assembly method.
Qualification: material identity, declarations, test reports, lot traceability and change control.

Use the six-step tubing selection guide to turn these factors into an RFQ. If two materials appear equivalent, compare total qualification and assembly risk rather than unit price alone.

Common Comparison Errors

Comparing a finished tube value with a raw film or resin typical value.
Using maximum temperature without time, load or test context.
Ignoring seams, adhesives, coating layers and winding overlap.
Treating chemical resistance as proof of low permeation or pressure capability.
Calling a product UL, FDA, RoHS or REACH compliant without product-specific evidence and scope.

Frequently Asked Questions

Is polyimide tubing always better than polyester tubing?

No. Polyimide may suit thinner walls or higher-temperature designs, while polyester film tubing may offer a better cost and process fit in less demanding conditions. Compare the finished construction, environment, tolerance and qualification requirements.

Can Nomex paper data be used as a tube specification?

Base-paper data helps screen the material, but a wound tube also depends on grade, layers, bond, seam, moisture, wall and manufacturing quality. Specify and test the finished tube characteristics that control the application.

When is PEEK justified?

PEEK is most defensible when its mechanical, wear, thermal or chemical properties solve a constraint that lower-cost materials cannot meet. Include qualification and processing cost in the comparison, not only raw-material price.

Which fluoropolymer is best for a clear fluid line?

FEP is often the first candidate when visual monitoring matters, but clarity depends on grade, wall, diameter and finish. Chemical, temperature, pressure and permeation requirements still need validation with an actual-size sample.

Request a Material and Process Review

Send WELLELE the application, drawing, operating environment and qualification requirements. WELLELE can compare feasible material and process routes subject to verified data and customer testing in the final assembly.

Submit your tubing specification for comparison.

Tubing Failure Analysis: A Practical Troubleshooting Guide

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Tubing Failure Analysis: A Practical Troubleshooting Guide

Tubing failure analysis should begin with the observed failure and service history, not with an immediate material change. Cracking, splitting, dielectric failure, loose fit, blockage, discoloration or leakage can originate from material selection, dimensions, manufacturing, storage, assembly or an operating condition that was missing from the original specification.

In this guide

Contain and preserve evidence
Link symptoms to causes
Eight-step analysis
Prevent recurrence
FAQ

First: Contain the Issue and Preserve Evidence

Separate affected and unaffected lots, record labels and quantities, and stop destructive handling of representative samples. Keep failed parts, unused tubing from the same lot, packaging and assembly records. Photograph the failure in place before removing the tube, because cut marks, routing, nearby edges and heat sources may explain the damage.

Record when the failure appeared: incoming inspection, cutting, insertion, winding, potting, thermal test, electrical test or field operation. A failure that occurs during insertion has a different evidence path from one that appears after months of thermal cycling.

Common Tubing Failure Symptoms and Likely Cause Families

Observed symptom	Possible cause families	Evidence to check
Longitudinal split or crack	Interference fit, low bend radius, embrittlement, cut damage, wrong material or ageing	ID distribution, insertion force, edge radius, temperature history, microscopy
Loose or slipping tube	Oversize ID, thermal relaxation, shrinkage assumption, lubricant or wrong tolerance	Before/after dimensions, mating-part range, temperature cycle, surface condition
Dielectric breakdown	Insufficient wall, pinhole, contamination, sharp edge, moisture or test mismatch	Failure location, wall map, surface, conditioning, voltage setup and applicable standard
Flattening or collapse	Vacuum, tight bend, compression, heat softening, packaging deformation	Ovality, bend radius, load, pressure/vacuum and storage stack
Leakage or permeation	Crack, poor fitting, chemical attack, pressure, permeation or wall variation	Joint, medium, concentration, temperature, wall, pressure history and leak test
Discoloration or residue	Overheating, contamination, reaction, adhesive migration or cleaning process	Temperature map, chemistry, lot comparison, surface analysis and process records
Blocked bore or high flow loss	Undersize ID, ovality, debris, kink, thermal deformation or coating buildup	ID profile, cleanliness, routing, cut end and flow/pressure data

These are hypotheses, not conclusions. Multiple mechanisms can create the same appearance, and one system can contain more than one contributing cause.

An Eight-Step Root-Cause Workflow

Define the failure precisely. Replace “tube is bad” with a measurable symptom, location, quantity and acceptance criterion.
Build the timeline. Record material receipt, storage, conversion, assembly, testing and service events.
Compare populations. Examine failed, non-failed same-lot, prior-lot and reference parts where available.
Verify identity and traceability. Confirm material grade, construction, supplier lot and any approved changes.
Measure against the drawing. Use an agreed method for ID, OD, wall, length, ovality, seam and surface.
Reconstruct the application. Include temperature, voltage or pressure, chemicals, bend, vibration, compression and duty cycle.
Test the leading hypotheses. Change one controlled factor at a time and use a method linked to the suspected mechanism.
Verify corrective action. Repeat the critical process and qualification cycle before closing the issue.

Measurement and Test Discipline

Agree on sample conditioning, instrument, location, contact force and calculation method before comparing results. Thin or flexible tubing can deform under measurement, creating apparent disagreements between customer and supplier. Read the technical data and test methods guide for a practical distinction between raw-material data, design qualification and lot inspection.

If the issue involves dimensions, link the analysis to the supplier’s dimensional inspection process. If material identity is uncertain, review material traceability and change records before running more tests.

How to Prevent Recurrence

Convert critical application conditions into drawing notes and supplier acceptance criteria.
Specify tolerances according to fit and function, not only nominal dimensions.
Approve a production-representative sample through the real assembly and duty cycle.
Define packaging, storage life, cleanliness and handling where deformation or contamination matters.
Require notification and requalification rules for material, tooling or process changes.
Retain samples and inspection records proportionate to failure risk.

Frequently Asked Questions

What should I send to a tubing supplier for failure analysis?

Send failed and unused same-lot samples, labels, drawing and revision, inspection data, assembly steps, service conditions, photographs and the exact failure rate. Do not clean, cut or mark every failed sample before the supplier reviews the evidence plan.

Does a dimensional result outside tolerance prove root cause?

It proves a specification nonconformance only if the measurement method is valid and agreed. It does not automatically prove that the dimension caused the field failure. Link the measured difference to a credible failure mechanism and controlled reproduction.

Should we change material after a crack?

Not until interference, sharp edges, bend radius, cutting, chemical exposure, ageing and actual temperature are checked. A stronger or more expensive material can fail again if the assembly mechanism remains unchanged.

What is the difference between containment and corrective action?

Containment protects current production by sorting or holding affected material. Corrective action removes a verified cause and prevents recurrence. A 100% sort can be valid containment but does not explain or eliminate the cause.

Request a Structured Failure Review

WELLELE can review available samples, drawings, lot information and application conditions to help define the next investigation step. The scope and test capability must be confirmed before analysis.

Submit the failure description and supporting evidence.

Tubing Engineering Calculations for Sizing, Fit and RFQs

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Tubing Engineering Calculations for Sizing, Fit and RFQs

Tubing calculations are useful for checking a specification, but they do not replace material, process or application validation. Engineers can calculate nominal wall thickness, diametral clearance, polymer cross-sectional area, percentage change and unit conversion from drawing dimensions. Pressure, dielectric and shrink performance require product-specific data and safety factors.

Worksheet sections

Basic tube geometry
Clearance and fit
Percentage change
Unit conversion
Calculation limits
RFQ worksheet

1. Nominal Wall Thickness

For a concentric tube defined by outside diameter (OD) and inside diameter (ID):

Nominal wall thickness = (OD - ID) / 2

Example: if OD is 2.00 mm and ID is 1.20 mm, nominal wall is (2.00 – 1.20) / 2 = 0.40 mm. This calculation does not prove actual minimum wall. If ID and OD tolerances stack in opposite directions, the minimum wall can be lower. Specify wall or concentricity directly when performance depends on it.

2. Diametral and Radial Clearance

For a tube sliding over a round component:

Diametral clearance = tube ID - maximum component OD
Nominal radial clearance = diametral clearance / 2

Use worst-case dimensions, not only nominal values. If tube minimum ID is 1.05 mm and component maximum OD is 1.00 mm, minimum diametral clearance is 0.05 mm. Assembly may still be affected by ovality, lead-in geometry, surface friction, bends and debris.

Fit question	Input needed	Additional check
Will the tube slide over the part?	Minimum tube ID and maximum part envelope	Ovality, entry chamfer, bend and insertion length
Will the tube stay located?	Maximum tube ID and minimum part OD	Thermal relaxation, adhesive, crimp or retention feature
Will a fluid fitting seal?	Tube ID/OD/wall and fitting specification	Material hardness, pressure, temperature and assembly method

3. Polymer Cross-Sectional Area

The nominal material area in a tube cross-section is:

Area = π / 4 × (OD² - ID²)

This can support relative material-use or weight estimates when density and length are known. It should not be used alone to estimate price because tooling, process speed, scrap, inspection, cut length and packaging can dominate cost.

4. Percentage Dimensional Change

For shrinkage, recovery or thermal dimensional change:

Percentage change = (final dimension - initial dimension) / initial dimension × 100%

A negative result indicates reduction. Define measurement direction, conditioning and datum. For heat-shrink products, free recovery is not the same as recovered dimensions over a component; wall growth, restraint and heat profile also matter.

5. Millimeter and Inch Conversion

1 inch = 25.4 mm
mm = inches × 25.4
inches = mm / 25.4

Do not round early. Convert the tolerance as well as the nominal dimension, and state which unit controls the drawing. Ambiguous mixed-unit specifications can cause avoidable inspection disputes.

What These Calculations Cannot Establish

Pressure rating: requires material allowables, temperature derating, geometry, fittings, duty and safety factor.
Dielectric rating: requires finished wall, material, defects, electrode setup, environment and standard.
Bend radius: depends on material, wall, temperature, ovality and whether the application is static or dynamic.
Thermal class: cannot be inferred from a short maximum-temperature exposure.
Chemical suitability: must include concentration, temperature, stress, time, permeation and joints.

Use the tubing selection guide before treating a calculated geometry as an approved design.

Copyable Tubing RFQ Worksheet

Field	Your requirement
Application and function	____________________
Material or allowed alternatives	____________________
ID / tolerance	____________________
OD / tolerance	____________________
Wall / tolerance	____________________
Length / cut tolerance	____________________
Continuous / peak temperature	____________________
Voltage, pressure or vacuum	____________________
Bend, abrasion and assembly	____________________
Quantity and annual demand	____________________
Required tests and documents	____________________

Frequently Asked Questions

Can wall thickness always be calculated from ID and OD?

The nominal wall can be calculated, but actual minimum and maximum wall depend on tolerance, concentricity and measurement. Specify wall directly if it controls dielectric, strength or fit.

How much clearance should a sleeve have?

There is no universal clearance. It depends on component tolerance, tube ovality, insertion length, bends, friction, cleanliness and whether the sleeve must remain fixed. Validate worst-case samples in the actual assembly.

Can these formulas calculate tube pressure?

No. Pressure design requires verified material strength at temperature, dimensions, fittings, duty, manufacturing quality and a design safety factor. Ask for a product-specific engineering review.

Should drawings use inches or millimeters?

Either is acceptable if one unit system controls, conversion is exact and tolerances are clear. Avoid dual dimensions that disagree after rounding.

Request a Size and Manufacturability Review

Send WELLELE your completed worksheet and drawing. Available sizes, tolerances and inspection methods remain subject to confirmed process capability.

Submit your calculated tube dimensions for review.

Tubing Technical Downloads: What Engineers and Buyers Actually Need

in resources

Tubing Technical Downloads: What Engineers and Buyers Actually Need

A useful tubing download center should help engineers select a product and help procurement qualify the supply. The core package normally includes a product datasheet, size or capability guide, application/RFQ form, inspection explanation and available compliance documents. Each file should identify its scope, revision date and whether data is typical or guaranteed.

In this guide

Document types
Read a datasheet correctly
RFQ package
Revision control
FAQ

How to Read a Tubing Datasheet

Check the product identity first. A resin, film or paper datasheet may be relevant but does not define a wound, coated or extruded tube. Look for specimen geometry, test method and conditions beside each property. “Typical” values support design screening; they are not automatic acceptance limits.

For dimensional capability, distinguish standard stocked sizes from custom development ranges. A size inside a broad capability envelope may still need tooling, minimum quantity and tolerance review. Use the tubing test-method guide to convert a datasheet into a controlled drawing and validation plan.

What to Include in the RFQ Package

Part drawing and revision, preferably with a neutral PDF plus native CAD where appropriate
Application and critical function
Material grade or approved alternatives
ID, OD, wall, length, tolerances and critical characteristics
Continuous and peak temperature; voltage or pressure/vacuum; chemicals and cleaning
Assembly, bend, abrasion, vibration and packaging requirements
Prototype quantity, production quantity and annual demand
Qualification, lot documents and change-notification requirements

A structured RFQ reduces quotation assumptions and later change orders. Download availability and WELLELE’s actual document set require `[CONFIRM: approved public files, revisions and document owners]`.

Revision and Evidence Control

Every public technical file should show a document title, identifier, revision, date and contact path. Retire obsolete downloads or clearly mark them superseded. If a compliance statement changes because a regulation, supplier declaration or material grade changes, update both the file and the web page.

Do not use an unqualified certificate logo as a substitute for the actual scope. Link readers to compliance document guidance and supplier qualification information for the evidence available with a quotation.

Suggested Download Cards for WordPress

Tubing RFQ Checklist: application and drawing input form. `[CONFIRM download URL]`
Material Comparison Chart: PI, Mylar-type polyester, Nomex-type aramid, PEEK and fluoropolymer screening. `[CONFIRM download URL]`
Dimensional Inspection Guide: ID, OD, wall and length method alignment. `[CONFIRM download URL]`
Product Datasheets: only approved material and tube documents. `[CONFIRM download URLs]`

Frequently Asked Questions

Is a TDS the same as a product specification?

No. A TDS usually presents typical or reference data. A product specification defines agreed requirements and acceptance limits for the supplied tube. Read the scope and status of every value.

Can I receive compliance documents before ordering?

Some declarations may be available during qualification, while lot-specific records are created after production. State the material, regulation, customer requirement and document type so scope and availability can be confirmed.

Why is a size chart not a quotation?

A chart shows a general capability or standard range. Price and manufacturability still depend on material, tolerance, tooling, length, inspection, quantity, packaging and delivery requirements.

What file format is best for a tubing drawing?

A controlled PDF is useful for quotation and revision reference. Add native CAD only when geometry or tooling review needs it. Ensure both files carry the same revision and dimensions.

Request the Correct Technical Package

Tell WELLELE the product, application and approval stage. The team can confirm which current datasheets, declarations, sample records and RFQ forms are available.

Request tubing technical documents.

Document	Decision supported	Scope to verify
Material or product datasheet	Initial material and performance screening	Grade, construction, units, test methods and typical/guaranteed status
Size/capability chart	Check whether a concept is manufacturable	Material, process, dimension range and whether tooling is required
Material comparison guide	Choose between PI, polyester, aramid, PEEK or fluoropolymer	Finished tube versus raw-material data and selection cautions
RFQ/application form	Collect inputs for a useful quotation	Dimensions, conditions, quantity, validation and documents
Inspection method guide	Align supplier and customer measurement	Instrument, conditioning, locations and calculations
Compliance declaration	Support regulatory or customer approval	Exact material/product, regulation version, exemptions and validity
Sample inspection report	Show record format before ordering	Redacted example only; not evidence for a different lot

Polyimide vs Kapton Tube: What’s the Difference?

Why the Confusion Exists

Quick Terminology Reference

What Is Polyimide (PI)?

What Is Kapton?

What Is a Polyimide Tube?

Kapton Tube vs Polyimide Tube: Key Differences

Film Data Is Not Tube Data

How to Choose: Kapton Tube or Generic PI Tube?

How to Write It Correctly on a Drawing

Common Specification Mistakes

FAQ

Is Kapton the same as polyimide?

Why is a Kapton tube also called a polyimide tube?

Can any polyimide tube be called a Kapton tube?

What temperature can Kapton withstand?

Is Kapton tube heat shrink?

Is extruded polyimide tube made from Kapton?

Engineering Recommendation

About the Author / Review

Sources

How to Select Insulation Tubing: A Six-Step Engineering Guide

Step 1: Define What the Tubing Must Do

Step 2: Map the Complete Operating Environment

Step 3: Shortlist the Material Family

Step 4: Specify Dimensions, Tolerance and Fit

Step 5: Match Material to Manufacturing Process

Step 6: Define Qualification Evidence Before the RFQ

RFQ checklist

Common Tubing Selection Mistakes

Frequently Asked Questions

What information is needed to select insulation tubing?

Should I specify ID and OD or ID and wall thickness?

Can the supplier recommend a lower-cost material?

When should I request a prototype?

Next Step: Request an Application Review

Tubing Technical Data and Test Methods: What Engineers Should Specify

Three Levels of Tubing Evidence

Dimensional Inspection: Define the Method

Electrical, Thermal, Mechanical and Fluid Tests

How to Build a Fit-for-Purpose Test Plan

What to Ask for in a Supplier Report

Frequently Asked Questions

Can I use a raw-material datasheet as the finished tubing specification?

Why do two laboratories measure different wall thickness?

How many samples should be tested?

Does a certificate of conformity include test data?

Request a Drawing and Test-Requirement Review

Related Engineering Guidance

Insulation Tubing Material Comparison: PI, Mylar, Nomex, PEEK and Fluoropolymers

Quick Engineering Comparison

When to Consider Polyimide Tubing

When to Consider Mylar-Type Polyester Tubing

When to Consider Nomex-Type Aramid Paper Tubing

When to Consider PEEK Tubing

When to Consider Fluoropolymer Tubing

A Five-Factor Selection Framework

Common Comparison Errors

Frequently Asked Questions

Is polyimide tubing always better than polyester tubing?

Can Nomex paper data be used as a tube specification?

When is PEEK justified?

Which fluoropolymer is best for a clear fluid line?

Request a Material and Process Review

Related Engineering Guidance

Tubing Failure Analysis: A Practical Troubleshooting Guide

First: Contain the Issue and Preserve Evidence

Common Tubing Failure Symptoms and Likely Cause Families

An Eight-Step Root-Cause Workflow

Measurement and Test Discipline

How to Prevent Recurrence

Frequently Asked Questions

What should I send to a tubing supplier for failure analysis?

Does a dimensional result outside tolerance prove root cause?

Should we change material after a crack?

What is the difference between containment and corrective action?

Request a Structured Failure Review

Related Engineering Guidance

1. Nominal Wall Thickness

2. Diametral and Radial Clearance