rigid, lightweight, cellular polystyrene, used in boat construction, insulation, commercial displays, etc.
Origin:
(poly)styr(ene) + -o- + foam
noun
this substance, or one like it
See Styrofoam in American Heritage Dictionary 4
A trademark used for a light, resilient polystyrene plastic. This trademark often occurs in print in lowercase: “throw-away plates, utensils and styrofoam trays”(Washington Post).