Styrofoam is a trademark of The Dow Chemical Company for closed-cell extruded polystyrene foam currently made for thermal insulation and craft applications. In 1941, researchers in Dow's Chemical Physics Lab found a way to make foamed polystyrene. Led by Ray McIntire, they "rediscovered" a method first discovered by Swedish inventor Carl Georg Munters. Dow acquired exclusive rights to use Munters' patents and found ways to make large quantities of extruded polystyrene as a closed cell foam that resists moisture.

Because of its insulating properties and buoyancy, it was adopted in 1942 by the United States Coast Guard for use in a six-person life raft.

Styrofoam has since found an immense variety of uses. Dow produces Styrofoam building materials, including insulated sheathing and pipe insulation. The claimed R-value of Styrofoam insulation is five per inch.

Dow also produces Styrofoam as a structural material for use by florists and in craft products. Dow insulation Styrofoam has a distinctive blue color; Styrofoam for craft applications is available in white and green.