In the world of foam, there are two main material varieties, open-cell and closed-cell. Almost every variety of normal foam can be placed into one of those two categories. Open-cell foam is soft and compressible, found in seat cushions and bedding, and the differences from one open-cell type to another are primarily in feel and durability. Closed-cell foam includes a much broader spectrum of materials, such as polystyrene, polyethylene, and neoprene. These foam types are so named because of their physical structure; open-cell foam’s cells are interconnected, while closed-cell foam’s cells are sealed off to one another.
One of the most unique closed-cell foams is also the most recognizable. Polystyrene is the white, rigid foam material used as home insulation, hot tub covers, and is formed into molded coffee cups and ice coolers. Expanded polystyrene (EPS) is almost totally resistant to moisture and will not rot, mold, or degrade from moisture or water vapor. It also possesses a strong R-value, a measure of thermal resistance and an important factor in the evaluation of insulation products.
Another noteworthy closed-cell foam, most neoprene features a matte, charcoal gray rubber color. In thicker cuts, it is able to function as mat camping pads and outdoor furniture pads, or when cut thinly, can be packed in a sheet roll for shipping and large purchases. Neoprene is soft, resilient, and also resistant to moisture, temperature extremes, and even Ozone. It can be used for stable but soft exercise mats, gardening knee pads, or even to cushion furniture at sporting events with cold, hard bleachers.
Polyethylene features what some consider a plastic feel and touts one of the largest cellular structures among foam materials in its high-density formulations. A superb packaging material, it has excellent vibration and shock absorption, and is able to be cut in thin sheets for wrapping items for shipping or storage. One of its most unique characteristics is its ability to be formed with anti-static compounds, resulting in a pink, static-dissipating material that guards sensitive electronics.