Compositions comprising (a) a monovinylidene aromatic polymer, e.g., HIPS, and (b) an ethylene/alpha-olefin (EAO) copolymer, e.g., an ethylene-propylene copolymer, that satisfies the mathematical relationship: y≦20+2.35x in which y is the ethylene content in mole percent (mol %) of the EAO copolymer and x is the Brookfield viscosity in centipoise (cP) at 10O° C. of the EAO copolymer and the viscosity is at least 1 centipoise (cP), exhibit improved environmental stress crack resistance as compared to compositions containing monovinyiidene aromatic polymers but without such an EAO copolymer. The compositions are useful in the manufacture of articles, e.g., refrigerator liners and food packaging, which come in contact with the oils contained in various food stuffs.

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