The morphology and mechanical properties of foams made out of a series of ethylene-alpha-olefin copolymers having well-characterized rheological properties were investigated. A compression foaming molding technique was implemented, using azodicarbonamide as the blowing agent. The polymers differed in the amount of comonomer contained (resulting in a range of densities), type of comonomer (octene vs. butene) and molecular weight, resulting in variable thermal properties and different rheological responses under shear and extensional flow. The results showed that the majority of the octene-based copolymers with comparable rheological properties had similar foam morphology. A distinct behaviour was observed for the butene-based copolymer, as well as the octene-containing one having the lowest density and lowest melting/crystallization points. The poor foamability of these grades was attributed to their differences in extensional and thermal properties, respectively. Increasing density resulted in a higher secant modulus of the foamed samples. POLYM. ENG. SCI., 51: 1145-1154, 2011. (C) 2011 Society of Plastics Engineers