Kapton® FN Polyimide Film

Kapton® FN is a heat-sealable composite film in which one or both faces of a Kapton® HN polyimide core are laminated with Teflon® FEP fluorocarbon resin. The polyimide core provides the thermal range, dielectric strength, mechanical toughness, and radiation resistance of standard HN; the FEP layer or layers add the ability to bond directly to adjacent film surfaces or copper by heat and pressure, without any adhesive. This eliminates intermediate bonding layers in magnet wire insulation, transformer coil wrapping, motor slot liners, and flex circuit assemblies — simplifying construction while maintaining the full Kapton® property profile.

FEP (fluorinated ethylene propylene) softens and flows under heat and pressure at temperatures well below the degradation point of the polyimide core, forming a direct bond to an adjacent surface when cooled. This means no separate adhesive film, no additional bonding step, and no adhesive layer contributing outgassing, thickness, or chemical incompatibility to the assembly. In high-density motor winding and magnet wire insulation, where every micron of added thickness affects slot fill and winding density, eliminating the adhesive layer is both a processing and a performance advantage.

The 120FN (0.030 mm) grade carries FEP on both faces and has the highest minimum dielectric breakdown in the range — the natural choice for fine magnet wire insulation where the thinnest heat-sealable structure is required and bilateral bonding is an advantage. The 150FN (0.035 mm) grade carries FEP on one face only, providing an asymmetric structure suited to applications where one side must seal and the other must present a bare polyimide interface. The 200FN (0.050 mm) grade is available in single- and double-sided FEP constructions and offers the greatest mechanical robustness and abrasion resistance — the correct choice for heavier motor and transformer winding applications where the thicker structure adds durability without compromising dielectric performance.

All three gauges are certified to MIL-P-46112B and ASTM D-5213. MIL-P-46112B is the US military specification for polyimide-fluorocarbon electrical insulation film, required for aerospace wire and cable insulation qualification. ASTM D-5213 is the standard specification for polyimide film used as electrical insulation, providing the traceable DuPont substrate baseline used in materials qualification programmes across motor, transformer, and aerospace applications. The UL thermal index for all gauges is 200–220°C for mechanical properties and 220–240°C for electrical properties under UL file E39505.

The Kapton® HN polyimide core maintains the full Kapton® family temperature range — continuous service from −269°C to +400°C. The FEP bonding layer has a lower continuous service limit, but all gauges carry the UL thermal index described above, confirming the sustained thermal endurance required in motor and transformer insulation systems. The shrinkage of the HN core is controlled to 2.5% maximum in both machine and transverse directions at 400°C, which confirms dimensional stability through thermal processing cycles.

Kapton® FN Film is used primarily in magnet wire insulation, where direct heat-seal bonding to copper without adhesive eliminates intermediate bonding layers; motor and transformer coil wrapping, where the FEP surface enables adhesive-free bond formation and the polyimide core provides the thermal endurance required at elevated winding temperatures; aerospace wire harness taping, where MIL-P-46112B certification and the non-stick, low-friction FEP surface meet aerospace electrical insulation specifications; and capacitor insulation, where high dielectric breakdown voltage, moisture absorption below 4%, and heat-seal capability support compact, reliable assembly.

Yes. ASTM D-5213 certification provides a traceable DuPont substrate baseline for heat-seal adhesion characterisation, dielectric breakdown measurement, and thermal lamination process development. Precision-cut flat pieces in the three gauges suit sample-scale testing across the full gauge range before committing to coil-based production processes.

Choose Kapton® FN whenever the assembly requires heat-seal bonding to adjacent film or copper surfaces without adhesive — magnet wire insulation, transformer coil wrapping, motor slot liners, and aerospace wire harness taping are the core use cases. Choose standard HN when no heat-seal bonding is required and the application needs only electrical insulation, thermal stability, or substrate performance — HN covers a wider thickness range and is the lower-cost option for applications where the FEP surface adds no functional value.

Kapton® FN Film is available in all three gauges in sizes from 10 mm × 10 mm up to 600 mm × 600 mm. Custom cut shapes, laser-profiled outlines, and non-standard sizes are available on request. Contact us with your gauge, dimensions, and required quantity.