the invention relates to a device and a method for welding two polymer parts via fusion using a heater mat knitted from a resistive wire coated with an insulating varnish , the heater mat being given a final shape . the heater mat is resistive wire having a diameter ranging from 0 . 2 mm to 0 . 3 mm , and has approximately parallelepiped meshes , the dimensions of which range from 1 . 5 × 3 mm 2 to 2 . 5 × 4 . 5 mm 2 .