Flexible heater device

A self-regulating flexible heater construction for producing heat when connected to an electrical power source comprises a flexible fabric substrate (10), a layer of a positive temperature coefficient (PTC) material (12), and a conductive material layer (14). The heating device includes a conductive layer which is positioned on an electrically insulative substrate. Preferably, the conductive layer is screen printed onto the substrate. The substrate is designed to limit elongation of the conductive layer, thereby improving the durability of the conductor and enabling the heating device to be used in flexible applications, such as automobile seats. The substrate can include at least one aperture passing therethough to further improve flexibility, fatigue resistance, and breathability of the heater. The conductive layer is configured to include a buss structure with a first buss ground inwardly adjacent from the periphery of the heating device and a first buss with serpentine paths extending from one edge of the heating device to another edge. The buss structure further includes a second buss with L-shaped portions positioned between the serpentine paths and the first buss ground. The second buss ground is located in a central location between the serpentine paths. A resistive or thermistor layer, preferably with a resistance which increases materially in response to increased temperature, is placed over the conductive layer.