AbstractThe UEWS test is described as a sensitive means to measure the stress in a material at which the first inelastic behavior becomes apparent. Particularly interesting observations have been made with PVC, where the aging of the material can be shown in a master curve diagram giving the relation between the UEWS and the age of the material at different molecular weights. Using this test as a tool, the performance of blends can also be measured. Blends of PVCs with different molecular weights and blends with various polystyrenes, polyvinyl acetate, and CPE are discussed.