The tensile and elastic properties of melt spun threads of segmented copolymers based on T6T6T-dimethyl (5-16 wt%) and PTMO1000/DMT of different lengths (3000-10,000 g/mol) are very good. Stress-strain measurements show that extruded threads of these polymers have high fracture strains ( > 1000%) and little strain hardening. The modulus and yield stress increase with increasing T6T6T content. The modulus decreases with increasing drawing-strain as a result of the breaking up of the crystalline network (strain softening). The compression set and tensile set increase with increasing T6T6T content and are low. The uniformity of T6T6T has little influence on the properties. At a soft segment length of 6000 g/mol a fibre with a tensile set of 5%, flow temperature of 200degreesC and rubber modulus of 7 MPa is feasible, which can compete with commercial materials. (C) 2003 Published by Elsevier Ltd.