Flexible heater watt density is meaningful only in context. A circuit bonded to a thick aluminum plate can reject heat very differently from the same circuit attached to plastic, wrapped around a pipe or exposed partly to air.
Use this guide to prepare a design review or RFQ. Final ratings depend on the complete product, installation, controls and operating environment.
Selection inputs that change the design
| Decision | Information to provide | Why it matters |
|---|---|---|
| Substrate | Material, thickness and thermal path | Controls heat spreading and local temperature. |
| Attachment | Bonded area, pressure and air gaps | Determines interface resistance. |
| Insulation | Back-side and surrounding insulation | Changes heat loss and warm-up. |
| Feedback | Sensor position and control method | Limits the temperature at the critical location. |
Calculate on the active area
Divide total power by the actual heated circuit area, excluding connectors, tabs and no-heat zones. Use consistent units and record whether the value describes the whole outline or active area.
A single average can hide concentrated traces or edge compensation. Ask for a circuit review when cutouts, clamps or heat sinks create nonuniform losses.
Model the complete thermal stack
List every layer between the resistance circuit and the controlled object, including adhesive, electrical insulation, interface pads and coatings.
Back-side insulation reduces loss but can also raise heater temperature. Review maximum temperature for the heater, adhesive, leads and substrate.
Control the hottest credible condition
Place feedback at the point that must be protected or controlled, and consider what happens if the heater lifts, the load is removed or ambient temperature rises.
Use an independent limit where overheating has significant consequences. Validate the design with temperature mapping during representative operation.
Common specification mistakes
- Using total outline instead of active area
- Ignoring adhesive and air gaps
- Adding insulation without reviewing heater temperature
- Testing only at the easiest operating condition
RFQ checklist
- Active heated area and circuit zones
- Substrate and interface layers
- Power, voltage and ambient range
- Insulation and mounting pressure
- Sensor, controller and fault conditions
Review the matching Flexible Heaters product range, then send this checklist with your drawing for an engineer-reviewed quotation.
Frequently asked questions
What watt density is safe?
There is no universal value. It depends on construction, substrate, contact, temperature and control.
Why do edges run hotter?
Edges may lose or spread heat differently, and partial bonding can concentrate temperature locally.
Should the sensor touch the heater?
Place it where it best represents the controlled or protected temperature, which may be the load rather than the heater face.