Two new methods have been developed for investigating the Young′s modulus and thermal conductivity of ultra oriented gel polyethylene films with draw ratios between 1 and 200.The laser generated ultrasonic pulse method gives the Young′s modulus in the draw and transverse direction

while the pulsed photothermal radiometry method gives the thermal conductivity in the draw

transverse and thickness direction of the film.The axial Young′s modulus is found to increase sharply with increasing draw ratio while the transverse modulus shows only a slight decrease.The thermal conductivity exhibits a similar behavior.At λ=200

the axial Young's modulus is about 80%of that of steel while the axial thermal conductivity is about twice that of steel. The great increases in the axial modulus and thermal conductivity arise form the presence of needlelike extended chain crystals (crystalline bridges). We propose a structural model which treats the crystalline bridges as the fiber phase of a short-fiber composite.This model provides a good description of the behavior of the axial Young's modulus and thermal conductivity.