Abstract: An insulation comprising a polyether polyester thermoplastic copolymer obtained by reacting 1, 4 butane diol terephthalate with terepthalate esters of polytetramethylene glycol is coated over an irregularly configured conductor, such as for example, a tinsel conductor, suitable for use in telecommunications cordage by moving the copolymer through an extruder and along a flow path formed between a core tube and wall of a die cavity. The die cavity adjacent to the throat of the die has a frustoconical portion formed with an approach angle of sufficient magnitude to minimize the pressure drop through the extruder to extrude the copolymer at a temperature slightly above the melting point of the copolymer.