A structural member is reinforced with a thermoset polymer foam having (a) a density of 80-650 kg/m3, (b) a storage modulus, measured on a 12 mm wide×3.5 mm thick×17.5 single cantilever sample according to ASTM D 4065-01, under conditions of 1 Hz and a heating rate of 2° C./min, such that the ratio of the storage modulus at 0° C., expressed in MPa, divided by the density of the thermoset polymer foam, expressed in kg/m3, is at least 0.4, and (c) the ratio of the storage modulus of the thermoset polymer foam at 100° C. divided by the storage modulus of the thermoset polymer foam at 0° C. is at least 0.5. The foam is preferably a polyurethane-isocyanurate foam. The foam exhibits excellent resistance to cracking due to mechanical and thermal stresses.