Kapton Heaters: Polyimide Etched-Foil Heating Elements

A Kapton heater earns its place wherever heat has to be added without anyone noticing the heater. The element is an etched metal foil sealed between two thin layers of polyimide film, so the finished part is only 0.2 to 0.3 mm thick and weighs almost nothing. It sits flat against a battery cell, an optical mount, a wafer chuck or an instrument wall without adding bulk and without holding warmth once the power is off. The foil does the heating and the film stores hardly any energy, so the part reaches temperature in seconds and follows a controller closely. That response, together with the very low outgassing of polyimide, is why these heaters turn up so often in vacuum, semiconductor, medical and battery work.

The range on this page is our standard program: a set of fixed sizes, two output levels and two backing options, all running on 12 V DC. It covers the parts most applications need off the shelf. When a standard part will not do, we build to drawing instead, with different shapes, higher surface loading, higher temperatures and mains voltage. If your part is in the range, order it. If it is not, the range is the place to start the conversation about the one you actually need.

What a Kapton heater actually is

The working part is an etched-foil resistive track laminated between sheets of polyimide film, the material most people know by DuPont's trade name, Kapton; the finished part is often called a polyimide film heater. That build is flexible but not elastic. The heater is happy wrapped around a cylinder or laid on a flat or single-curve surface, but it must never be forced onto a compound or spherical shape, or onto anything that grows and shrinks underneath it, because the foil circuit eventually cracks where it is stretched. Continuous immersion is a similar caution: water finds its way in at the laminated edges over time, so anything submerged is worth discussing as a custom build rather than treating as a stock use.

Kapton or silicone?

Flexible surface heaters come in two materials, and they are not really competitors. Kapton is thin, fast, light and silicone-free, but the foil circuit is fragile and will not take a compound curve. Silicone rubber is thicker and slower to react, yet it shrugs off the handling that a workshop or a drum wrap involves. The table compares them on the points that decide a job rather than the ones that fill a brochure.

Kapton (polyimide) Silicone, wire-wound Silicone, etched-foil
Continuous temperature −40 to +200 °C −60 to +250 °C −60 to +200 °C
Continuous temp, self-adhesive −40 to +180 °C n/a n/a
Thickness / build height 0.2 to 0.3 mm 1.1 to 3 mm 0.8 to 1.5 mm
Largest single sheet up to 285 × 550 mm 940 × 3000 mm 595 × 2500 mm
Max surface loading 0.8 W/cm² in open air about 0.8 W/cm² about 0.8 W/cm²
Thermal mass and response Lowest, fastest Higher, slower Medium
Mechanical handling Delicate, single curves only Rugged Rugged
Vacuum, low outgassing Yes, low CVCM No No
Silicone-free Yes No No
UL and VDE versions Not available Available Available

Silicone figures above are typical for the material class; see the silicone heaters page for exact specifications.

If the heater has to disappear into an assembly, react quickly, work under vacuum or stay clear of a silicone-sensitive process such as paint preparation or optics, Kapton is the right call. For drums, IBCs, gas cylinders or anything that takes rough use, a silicone heater is the better tool, and plenty of builds use one of each: polyimide on the sensitive part, silicone on the bulk vessel.

How much heat it can take

Watt density, or surface loading, is the number that decides whether a polyimide heater lasts. The stock range here stops at 0.6 W/cm², and 0.8 W/cm² in open air is the recommended ceiling for any flexible heater, Kapton or silicone alike. You can go higher, but only when the heat has somewhere to escape. Bonded to a metal plate and run under a fast controller, a custom heater can reach 2 to 3 W/cm². The detail that catches people out is that a thermostat reads the temperature of the foil itself, not of whatever you are heating, so a heater that is poorly bonded shows a controller a low reading while the element quietly cooks itself. High surface loading without a heat path is the usual way these parts fail.

Mounting and temperature

The film itself runs from −40 to +200 °C, but how you hold the heater sets the real limit. The self-adhesive backing, a low-outgassing pressure-sensitive adhesive, is good to about 180 °C and covers most mounting jobs. The plain, non-adhesive version is used up to 200 °C, held against the surface by a clamp; for that, and for any higher-temperature custom build, the heater is clamped between metal plates with a thin silicone buffer, around half a millimetre, to spread the clamping load and keep the etched circuit from being crushed. Copper or aluminium plating, and adhesive-less all-polyimide construction, push the working temperature toward 260 °C, and both of those are custom territory.

Vacuum and low outgassing

Low outgassing is the property that sells a polyimide heater into the cleanest jobs, so it is worth stating in numbers rather than adjectives. Tested to ASTM E595, the self-adhesive construction returns collected volatile condensable material of 0.02 percent, a total mass loss of 1.54 percent and water vapour regained of 0.64 percent. The figure that governs whether a heater leaves a film on the surfaces around it is the condensable material, and 0.02 percent sits well inside the 0.10 percent limit used to judge that, which is what makes the standard part a sound choice for vacuum chambers, semiconductor tools and other clean processes. Total mass loss is the stricter screen: at 1.54 percent it is above the 1.0 percent line that flight-qualified space work asks for, so for satellite and space applications we specify a low-TML custom construction rather than the stock part.

What it takes to run one

These are 12 V DC component heaters, not appliances you plug into a wall. To put one to work you need a DC supply matched to the load, and a thermostat or controller with a sensor. The supply matters more than it first looks: the 45 W part pulls 3.75 A, and that current sets both the rating of the power supply and the gauge of the wiring. The control matters because a bare resistive heater regulates nothing on its own and will overshoot if it is left to itself. The trade-off is worth it, because 12 V is extra-low voltage, which means the heater carries no shock risk and needs no electrical approval on the element, and that is exactly why polyimide heaters are trusted in wet, laboratory and medical settings. If you need a mains-voltage version at 115 or 230 V, that is a custom build.

When the standard range is not enough

The stock program covers 12 V up to 0.6 W/cm². Past that, we engineer the part to suit. That covers higher surface loading of 2 to 3 W/cm² with the heat path designed in, higher temperatures toward 260 °C using plated or all-polyimide construction, mains voltage, shapes with holes, cut-outs and slots, and sensors or thermostats built into the heater itself. If any of that describes your job, tell us what you need and we will quote it.

Where they are used

Typical work includes warming electric-vehicle and equipment batteries, semiconductor and wafer handling, medical devices and diagnostics, optics and display assemblies, laboratory instruments, telecom enclosures, anti-condensation and defrost duties, and aerospace, satellite and vacuum systems. The thread running through all of them is a sensitive component, a tight space or a process that cannot tolerate contamination, the cases where a thin, fast, clean foil heater beats a heavier one. For larger or more rugged heated surfaces, such as drums, IBCs and gas cylinders, our silicone heaters are the better starting point.