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An article, preferably an insulated food serving unit such as a tray or a tray cover, having a top shell and a bottom shell which are physically interlocked with a snap-fit connection. A rigid, substantially dimensionally stable foam between the top and bottom shells locks the shells together, seals

An article, preferably an insulated food serving unit such as a tray or a tray cover, having a top shell and a bottom shell which are physically interlocked with a snap-fit connection. A rigid, substantially dimensionally stable foam between the top and bottom shells locks the shells together, seals the snap-fit connection and provides rigidity to the overall article. Reinforcing ribs may be used to decrease flexure at the connection seam and protect the foam against impact at the connection seal.

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An insulated, plastic food serving unit formed of two interlocking parts and a rigid, expanded foam, said unit comprising: a top shell made of a material comprising a polyolefin, polyolefin copolymer, halogenated polyolefin, copolymer of halogenated polyolefins, acetal, or nylon and exhibiting a gen

An insulated, plastic food serving unit formed of two interlocking parts and a rigid, expanded foam, said unit comprising: a top shell made of a material comprising a polyolefin, polyolefin copolymer, halogenated polyolefin, copolymer of halogenated polyolefins, acetal, or nylon and exhibiting a generally planar top surface, top shell sidewalls oriented generally transverse to said top surface, and a top shell rim attached to said to shell sidewalls, said top shell rim exhibiting an interlockable hook-shaped configuration; a bottom shell made of a material comprising a polyolefin, polyolefin copolymer, halogenated polyolefin, copolymer of halogenated polyolefins, acetal, or nylon and exhibiting a generally planar bottom surface, bottom shell sidewalls oriented generally transverse to said bottom surface, and a bottom shell rim attached to said bottom shell sidewalls and exhibiting an undercut-shaped configuration that is physically interlocked with the top shell rim, said top surface being spaced apart from the bottom surface by a vertical distance and defining an enclosed interior volume bounded by interior surfaces of the top surface, the bottom surface, and the sidewalls of the top and bottom shells that are interlocked at their rims; whereby at least a portion of the interior top shell surfaces, at least a portion of the interior bottom shell surfaces, or at least a portion of both the top and bottom shell interior surfaces are treated by flame etching, chemical etching, and/or corona discharge to increase the chemical bonding capabilities of the treated interior surfaces; and whereby said top shell rim or said bottom shell rim exhibit vent slots: means for reinforcing the top shell sidewalls, the bottom shell sidewalls, or both the top and bottom shell sidewalls against lateral flexure, said means for reinforcing comprising at least one reinforcement rib that extends away from the top shell sidewall for a predetermined distance as an integral part of said top shell; and an expanded foam within said enclosed interior volume and chemically bonded to substantially all of said interior surfaces sealing said vent slots, and positioned to force together the interlockable shape of said top shell and the mating shape of said bottom shell to fix said top shell to said bottom shell in a secure configuration.