View Latest Blog Entries
Testing & Assessment Certification Aging Wires & Systems Standard & Regulation Management Conference & Report Maintenance & Sustainment Protection & Prevention Research Arcing Miscellaneous
Popular Tags
Visual Inspection MIL-HDBK MIL-HDBK-525 AS50881 FAR High Voltage FAR 25.1707 Electromagnetic Interference (EMI) Maintenance Wire System Arcing Damage Degradation
All Tags in Alphabetical Order
25.1701 25.1703 Accelerated Aging ADMT Aging Systems Aircraft Power System Aircraft Service Life Extension Program (SLEP) arc damage Arc Fault (AF) Arc Fault Circuit Breaker (AFCB) Arc Track Resistance Arcing Arcing Damage AS22759 AS22759/87 AS4373 AS4373 Method 704 AS50881 AS5692 AS6019 AS83519 AS85485 AS85485 Wire Standard ASTM D150 ASTM F2799 ATSRAC Attenuation Automated Wire Testing System (AWTS) batteries Bent Pin Analysis Best of Lectromec Best Practice bonding Cable cable testing Carbon Nanotube (CNT) Certification Chafing Chemical Testing Circuit Breaker circuit design Circuit Protection Coaxial cable cold bend comparative analysis Compliance Component Selection Condition Based Maintenance Conductor conduit Connector connectors contacts Corona Corrosion Corrosion Preventing Compound (CPC) Cracking D-sub data analysis data cables degradat Degradation Delamination Derating diagnostic dielectric constant Distributed Power System DO-160 Electrical Aircraft Electrical Component Electrical Testing Electromagnetic Interference (EMI) Electromagnetic Vulnerability (EMV) EMC EMF EN3197 EN3475 EN6059 End of Service Life End of Year Energy Storage engines Environmental Environmental Cycling ethernet EWIS Component EWIS Design EWIS Failure EWIS Thermal Management EZAP FAA AC 25.27 FAA AC 25.981-1C Failure Database Failure Modes and Effects Analysis (FMEA) FAQs FAR FAR 25.1703 FAR 25.1707 FAR 25.1709 fault tree Fixturing Flammability fleet reliability Flex Testing fluid exposure Forced Hydrolysis fuel system fuel tank ignition functional testing Fundamental Articles Future Tech Green Taxiing Grounding Harness Design Hazard Analysis health monitoring heat shrink tubing high current high Frequency high speed data cable High Voltage History Hot Stamping Humidity Variation ICAs IEC60172 Instructions for Continued Airworthiness Insulation insulation resistance IPC-D-620 ISO 17025 Certified Lab Kapton Laser Marking life limited parts life projection Lightning Maintenance Maintenance costs Mandrel Mechanical Testing MECSIP MIL-C-38999 MIL-C-85485 MIL-DTL-17 MIL-DTL-3885G MIL-DTL-38999 MIL-E-25499 MIL-HDBK MIL-HDBK-1646 MIL-HDBK-217 MIL-HDBK-454 MIL-HDBK-516 MIL-HDBK-522 MIL-HDBK-525 MIL-HDBK-683 MIL-STD-1560 MIL-STD-1798 MIL-STD-464 MIL-T-7928 MIL-T-81490 MIL-W-22759/87 MIL-W-5088 Military 5088 modeling MS3320 NASA NEMA27500 No Fault Found off gassing Outgassing Overheating of Wire Harness Parallel Arcing part selection Performance physical hazard assessment Physical Testing polyimdie Polyimide-PTFE Power over Ethernet Power systems predictive maintenance Presentation Probability of Failure Product Quality Radiation Red Plague Corrosion Reduction of Hazardous Substances (RoHS) regulations relays Reliability Research Rewiring Project Risk Assessment SAE Secondary Harness Protection Separation Requirements Series Arcing Service Life Extension Severe Wind and Moisture-Prone (SWAMP) Severity of Failure Shield Shielding signal cable silver plated wire smoke Solid State Circuit Breaker Space Certified Wires Splice standards stored energy supportability Sustainment Temperature Rating Temperature Variation Test methods Test Pricing Testing Thermal Circuit Breaker Thermal Endurance Thermal Index Thermal Shock Thermal Testing Tin plated conductors Troubleshooting TWA800 UAVs verification Visual Inspection voltage white paper whitelisting Wire Ampacity Wire Certification Wire Comparison wire damage wire failure wire properties Wire System wire testing Wire Verification work unit code

Should Polyimide Insulated Wire be Trusted?

Testing & Assessment

Key Takeaways
  • Polyimide (common trade name Kapton) has been a go-to insulation type for aerospace for nearly five decades.
  • Polyimide insulated wires often show good performance in flame resistance and mechanical tests.
  • Incidents have cast a shadow over the material even though its use and base material have improved significantly since the mid-1990s.
  • Listen to the podcast here.

The history of polyimide insulated wire is one that has numerous opinions and a lot of misconceptions. After several incidents involving polyimide wire in military and commercial aircraft, many within the aerospace industry refused to put any polyimide insulated wire/cable onto the aircraft they design/maintain. As is often the case with components involved in incidents, a lot of facts and myths get jumbled together.

To help shine light on the topic, we look to cover the history of polyimide (both the good and bad) and the potential future of the material in aircraft systems.

Where Did It Come From?

The polyimide material was invented in 1955 and it was immediately identified as great insulating material with excellent mechanical properties. Other strengths of polyimide include its fantastic resistance to flame, performance in radiation intense environments (those who remember the Voyager spacecraft will recall a lot of the amber colored coatings on the vehicle, this is polyimide), and the great physical toughness. These properties were advantageous for several applications including circuit boards.

Seeing the benefits of this material as an insulator, manufacturers sought to take the polyimide material, manufacture a tape, and wrap it around a conductor to create a wire. Given the aforementioned mentioned properties of polyimide, this was a natural progression for the material.

EWIS Failure Rate Breakdown
Failure modes of EWIS components. Source: Navy Safety Center Hazardous Incident Data 1980 – 1999.

Chafing damage to wire/cable insulation are a primary mode of failure for wiring components. The physical toughness was (and still is) a huge selling point of polyimide; among the common aircraft wire insulation materials (PTFE, ETFE, and Polyimide), polyimides ability to endure extended durations of chafing is an easy sell.

Polyimide became quite a popular material and could be found within numerous vehicles (military, commercial, etc.); and then the problems began (Lectromec has covered several of the incidents and problems with polyimide in papers and articles). In summary, the polyimide polymers degrade very quickly when exposed to a combination of heat, humidity, and mechanical strain. This degradation is greatly accelerated when formed into a thin tape tightly wrapped around a conductor.

Unfortunately, this degradation mechanism was not anticipated as there were no specific testing outlined in the product qualification standard that would identify this problem. In application, some of the polyimide wires degrade very quickly and lead to electrical arcing events. Polyimide film wire is extremely susceptible to carbon arc tracking.

Material Improvements

In the early 90s, the threat posed by polyimide was well-established and began to become a feared wire for use on aircraft. This is reflected in the ban the Navy placed on installing polyimide wire for new aircraft applications in 1992. Similarly, OEMs and maintainers began to look for alternatives to polyimide insulated wire but did not want to lose the mechanical performance polyimide provided.

Wire manufacturers saw the positive elements of polyimide wire and worked with the polymer manufacturers to develop improved materials and wire constructions. By the end of the 90s, the polyimide tape used for wire insulation had an additional coating on the tape to make it less susceptible to degradation in high humidity environments. To further reduce the exposure of the polyimide insulation to humidity, wire constructions paired polyimide with a PTFE top layer; this PTFE top layer also helps to reduce the threats from arc tracking.

Modern Applications

Today, there are a wide range of wire constructions that include a layer of polyimide and PTFE. This provides the combined benefits of polyimide’s mechanical-strength/abrasion-resistance and the fluid resistance of PTFE. Further, these are one of the few construction types of wire that can perform well in high temperature environments (up to 260°C).

The Threat to Aircraft

It is important to realize that polyimide insulated wire, when used properly and with good wire constructions, is not a threat to modern aircraft. Modern wire constructions that employ the combination of polyimide and PTFE (e.g. AS22759/80 – /92 and /180 – /192) require qualification testing to determine their arc track susceptibility (e.g. AS4373 Method 508 and 509). These wire constructions have tight performance requirements permitting only a few wires to fail the post-test dielectric evaluation.

Further, advanced circuit protection devices, such as arc fault circuit protection  or solid-state power controller with advanced circuit protection algorithms, go a long way to reducing the threats from electrical arcing. Modern aircraft design is progressively more dependent upon the integration of systems.

The wiring system and individual components performance requirements should be reviewed. Does it make sense to have such high standards on the arc fault performance of a wire when it is paired with a device that should, in theory, reduce the electrical arcing event duration to less than 10% of what is possible in an event using the thermal circuit protection? The answer to questions like this will define the next generation of EWIS.


The polymer known as polyimide has great mechanical properties for an insulator and is a good choice for wire insulation. While the past of this material is not without issue, employing wire constructions with this material for modern application is entirely reasonable. But to do so requires verification of the wire/cable performance through methodical testing and analysis.

Michael Traskos

Michael Traskos

President, Lectromec

Michael has been involved in wire degradation and failure assessments for more than a decade. He has worked on dozens of projects assessing the reliability and qualification of EWIS components. Michael is an FAA DER with a delegated authority covering EWIS certification and the chairman of the SAE AE-8A EWIS installation committee.