Interpolymer resin particles that include from about 20% to about 60% by weight based on the weight of the particles of uncross-linked polyolefin resin particles having a VICAT softening temperature greater than 85° C. and from about 40% to about 80% by weight based on the weight of the interpolymer particles of polymerized vinyl aromatic monomer composition particles that have been polymerized in the uncross-linked polyolefin resin particles to form an interpenetrating network of polyolefin resin particles and polystyrene particles. The interpolymer resin particles have a gel content ranging from about 0 to about 1.5% by weight based on the weight of the interpolymer resin particles, a VICAT softening temperature ranging from about 90° C. to about 115° C., and a melt index value ranging from about 0.2 to about 35.0 g/10 minutes (Condition G).