1950, trademark name (Dow Chemical Co.), from -styr- (from polystyrene) + connective -o- + foam (n.).
Entries linking to styrofoam
polystyrene n.
hard, colorless thermoplastic resin, 1922, so called because it is a polymer of styrene.
foam n.
Middle English fom, fome (c. 1300), from Old English fam "foam, saliva froth; sea," from West Germanic *faimo- (source also of Old High German veim, German Feim), from PIE root *(s)poi-mo- "foam, froth" (source also of Sanskrit phenah; Latin pumex "pumice," spuma "foam;" Old Church Slavonic pena "foam;" Lithuanian spainė "a streak of foam"). The plastic variety used in packaging, etc., so called from 1937.