Foamed plastic, synthetic resin converted into a sponge like mass with a closed-cell or open-cell structure, either of which may be flexible or rigid, used for a variety of products including cushioning materials, air filters, furniture, toys, thermal insulation, sponges, plastic boats, panels for buildings, and even lightweight beams. Under appropriate conditions almost any thermosetting or thermoplastic resin can be converted into foam. Plastics that are commonly foamed include vinyls, polystyrene, polyethylene, phenolics, silicones, cellulose acetate, and urethanes.
Foams with a closed-cell structure are produced by incorporating a blowing agent that decomposes at the fusion point of the plastic, releasing gas bubbles that are trapped during the gelling. Foams with an open-cell structure are produced by incorporating an inert gas into the resin under pressure and then releasing the mixture to the atmosphere and curing the resulting foam.
Bubbles and air can be put into plastics to turn them into foams and lightweight plastics. Sometimes the bubbles are big enough to see. In other cases they are microscopic. Plastic foams have a number of uses. They are excellent materials for making packaging like cartons for foods and delicate items which need protecting from knocks.
Rigid foam is mainly used as a heat insulator. It is injected into the spaces between the outer walls of houses to keep them warmer. Some plastic foam can be toxic due to the chemicals involved in making them. Now, many foams are made which are less toxic.