A layer is only one part of the heat pathRT/duroid 6035HTC. Engineering illustration, not a production photograph or test result.A layer is only one part of the heat pathRT/duroid 6035HTCDevice / heat sourceAttachment interfacePCB dielectric and copperContact / bond to supportHeat spreader or sinkRtotal includes layers, interfaces, spreading and the environment.One-dimensional layer model: R = t / (k × A). Not a device temperature.