We report the development of highly chemically crosslinked, ultra low density (similar to 0.015 g/cc) polyurethane shape memory foams synthesized from symmetrical, low molecular weight, and branched hydroxyl monomers. Sharp single glass transitions (Tg) customizable in the functional range of 4570 degrees C were achieved. Thermomechanical testing confirmed shape memory behavior with 9798% shape recovery over repeated cycles, a glassy storage modulus of 200300 kPa, and recovery stresses of 515 kPa. Shape holding tests under constrained storage above the Tg showed stable shape memory. A high volume expansion of up to 70 times was seen on actuation of these foams from a fully compressed state. Low in vitro cell activation induced by the foam compared with controls demonstrates low acute bio-reactivity. We believe these porous polymeric scaffolds constitute an important class of novel smart biomaterials with multiple potential applications. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012