The Young’s modulus and loss tangent have been measured in air for a number of commercially available polyurethanes. A resonance technique was used for measurements over the approximate frequency range 102to 104Hz and the approximate temperature range 40° to −5 °C. Master curves and Williams–Landel–Ferry shift constants were detemined for the materials tested. The automated data acquisition system used is described. The experimental procedure was found to be a reliable method for determining the viscoelastic constants for extensional wave propagation in elastomeric materials.