What are the two types of foam?

Two main types of foam by cell structure are open cell foam and closed cell foam, which differ in how air is trapped inside. Open cell foam has cells that are interconnected and not fully enclosed, making it soft, flexible, breathable, and able to absorb water, examples include memory foam, flexible polyurethane foam used in mattresses and sofa cushions, and acoustic foam. Open cell foam is softer, lighter, less expensive, and allows air and moisture to pass through. Closed cell foam has cells that are completely enclosed and sealed, making it rigid, firm, water resistant, and better insulating, examples include rigid polyurethane foam insulation, extruded polystyrene XPS, polyethylene foam used in packaging, and foam boards. Closed cell foam is harder, more durable, more expensive, provides higher R-value per inch for insulation, and resists water. So two fundamental types are open cell soft foam for cushioning and closed cell rigid foam for insulation and structural support, each serving different applications based on softness and moisture resistance.