Polyimide (Kapton): Weight Savings vs. Arc-Tracking
The complicated history and modern application of aerospace's lightest, most controversial wire insulation.
Few materials in aerospace engineering have a more storied—and polarizing—reputation than Polyimide tape insulation, most famously known by DuPont's trade name, Kapton®. In the 1970s and 80s, it was hailed as a miracle material. Today, its use requires careful specification.
The Appeal: Unmatched SWaP Benefits
In aerospace, SWaP (Size, Weight, and Power) is everything. Polyimide delivers extraordinary dielectric strength, meaning the insulation wall can be incredibly thin while still blocking high voltages.
By switching an airframe from older, thick-walled insulations to Polyimide, manufacturers could save hundreds of pounds per aircraft and significantly reduce the diameter of wire bundles, freeing up valuable space in conduits.
The Danger: Arc-Tracking
However, pure Polyimide insulation has a fatal flaw: when it degrades (due to chafing, mechanical damage, or extreme age) in the presence of moisture, a small electrical short can carbonize the polyimide material.
Carbon is conductive. This creates a conductive path (a "track") across the insulation, leading to a massive, self-sustaining electrical arc. This phenomenon, known as arc-tracking or "flashover," can literally vaporize adjacent wires in a bundle, causing cascading electrical failures and catastrophic fires. High-profile incidents in the 1990s led the military and commercial sectors to severely restrict the use of pure Polyimide wire.
Modern Solutions: Composite Tape (TKT)
The aerospace industry didn't want to give up the weight savings of Polyimide, so material scientists developed composite insulations. The most common solution is TKT (Teflon-Kapton-Teflon) or similar polyimide/fluoropolymer composites.
By sandwiching the Polyimide layer between thin layers of PTFE (Teflon), the wire retains the extreme thinness and weight savings of Kapton, but the outer PTFE layer provides high resistance to chafing, moisture ingress, and ultimately eliminates the risk of arc-tracking.
Modern Specifications: When engineers want the benefits of Polyimide today, they specify composite wires such as MIL-W-22759/80 through /92 (AS22759/80-92), which offer the best of both worlds: extreme light weight, high temperature resistance (up to 260°C), and safety from arc-tracking.