US Patent 11472134 Electrothermal heater mat

In manufacturing an electrothermal heater mat, there is provided a preform which comprises a laminated stack of dielectric layers which are made of thermoplastic material and include a central layer or group of layers which include(s) reinforcement and first and second outer groups of layers which do not include reinforcement. The preform includes a heater element and the preform has a first configuration. The preform is then heated to a temperature (e.g. 180° C.) between the glass-transition temperature of the thermoplastic material and the melting point of the thermoplastic material, and the heated preform is formed into a second configuration which is different to the first configuration so as to produce the heater mat.