What is the strongest type of foam?

The strongest type of foam is typically high-density closed-cell rigid foam such as closed-cell polyurethane foam, high-density EVA foam, or extruded polystyrene foam with high compressive strength, measured by pounds per square inch that it can support without deforming, similar to strong Packout box material. Among flexible foams, strongest is high-density polyurethane foam with density 2.5 to 3.0 pounds per cubic foot and ILD over 50, which provides very firm support and resists compression, used for heavy-duty seating and orthopedic support. Among rigid foams, strongest is structural polyurethane foam with density 8 pounds per cubic foot or more, used for construction panels, boat hulls, and insulation that can support significant load. For example, high-density closed-cell spray foam with 2 pounds per cubic foot has compressive strength of 25 to 30 psi, able to support weight and resist moisture, stronger than open-cell foam which is only 3 to 5 psi. EVA foam with Shore hardness 60 plus is very strong for protective gear. So strongest type of foam is high-density closed-cell rigid polyurethane or extruded polystyrene foam with high density and compressive strength, providing structural strength, water resistance, and durability for construction and industrial applications, opposite of soft low-density foam.