Ray McIntire, a former chemical engineer for the Dow Chemical Co. who invented by accident the material known today as Styrofoam, died on Friday at his home in Midland, Mich. He was 77.

In an interview in 1993, McIntire said he was trying to develop a rubberlike polymer to be used as a flexible insulator. He combined styrene with isobutylene, a volatile liquid, under pressure. When the pressure was released, McIntire discovered that the styrene had formed a polymer but the isobutylene had not. Instead, the isobutylene evaporated and made a foam polystyrene with bubbles in it. It was 30 times lighter and more flexible than the polystyrene that had previously been used.

Beginning after World War II, Dow Chemical sold the product for use as building insulation under the trademark Styrofoam. Today, the name has become synonymous with all rigid foam products.