Bonded urethane foam, also known as rebond, is the most common type of carpet pad material. About 80 percent of pads sold are made of bonded foam, which is constructed of foam scraps left over from the manufacture of furniture, mattresses and automobile components [source: Carpet Information]. It may also come from scrap generated by the foam-making process and can include recycled, post-consumer foam.
The foam scraps are chipped into small pieces and then fused using either adhesive or a heat process. The foam is then bonded to fabric, net or plastic film to give the pad more strength and to make it easier to handle. Bonded urethane carpet pads use a great deal of foam that would otherwise go to waste, so the price tends to be low. Of course, prices will fluctuate with scrap foam's market value.
A bonded pad is versatile and can be a good choice for most situations, as long as you avoid padding that's too thick. The Carpet and Rug Institute advises that no pad should be more than seven-sixteenths of an inch [source: Carpet and Rug Institute]. In part, this is because a thick pad allows too much up-and-down movement of the carpet, wearing the backing as it flexes. Also, a pad that's too thick can allow the carpet to pull away from the tack strip that holds it flush with the wall.
The minimum HUD standards for bonded urethane foam are 0.375 inch (9.525 millimeters) and 5 pounds per cubic foot (about 80 kilograms per cubic meter) for light or moderate traffic areas, and the same thickness requires 6.5-pounds-per-cubic-foot (104-kilograms-per-cubic-meter) foam for heavy traffic [source: CarpetInspector.com]. Many professionals and carpet manufacturers recommend even denser foam, especially for hallways. Foam in weights from 7.5 to 8 pounds per cubic foot (120 to 128.1 kilograms per cubic meter) will hold up better and help protect your carpet.
Remember that bonded foam will not hold up as long as premium pads like frothed foam or rubber. Some carpet retailers sell inferior bonded urethane foam that may lack the proper density for your specific application. Another concern with bonded foam is the out-gassing of butylated hydroxytoluene (BHT). This chemical was once added to urethane foam to reduce its flammability. It can yellow carpet, especially light-colored olefin. Bonded foams are less likely to contain BHT today, but make sure the seller guarantees it will not harm your carpet [source: Carpet Buyers Handbook].
On the next page you'll read about the pad that gives your carpet maximum support.