ANISOTROPIC POLYURETHANE FOAM WITH POISSONS RATIO GREATER-THAN-1

Anisotropic polymer foams have been prepared, which exhibit a Poisson' s ratio exceeding 1, and ratios of longitudinal to transverse stiffnes s exceeding 50. The foams are as much as 20 times stiffer in the longi tudinal direction than the foams from which they were derived. The tra nsformation process involved applying to open-cell polyurethane foam a n axial strain of 25 to 45%, at a temperature above the softening poin t, followed by cooling under axial strain.