Upholstery foam is any foam used as padding in fabric-covered, or upholstered, furniture. Most upholstery foam is flexible polyurethane foam (FPF) although latex foam is also used. Different types of upholstery foam are used for indoor, outdoor and marine furniture. Multiple types of upholstery foam may be used in a single piece of furniture. For example, foam used in seat cushions is different than the foam used for the back of a chair. Foam can be purchased in sheets, or cut to size.
Polyurethane foam is created through a chemical reaction of urethane and water. Most upholstery foam is manufactured using the slabstock process. A mixture of the two chemicals that make up the urethane, polyol and diisocyanate, are mixed with water and poured onto a conveyor with sides that are between three and four inches (7.62 and 10.16 cm) high. As the chemicals react, the mixture expands into a slab which is then cut, stored and cured for up to 24 hours.
Upholstery foams have density ratings which are directly related to the ratio of urethane chemicals and water used to manufacture the foam. The more urethane it has relative to water, the denser the foam will be. In furniture, higher density foams will last longer because they will retain their shape longer over time. Higher density upholstery foam is more expensive than low-density foam because greater amounts of urethane are used during the manufacturing process. In addition to density, upholstery foam is rated by indentation load deflection (ILD). The indentation load for a given piece of foam is the amount of pressure it takes to compress the foam to 25 percent of its original thickness.
Replacing the foam in your upholstered furniture can add years of life to it, and may be much less expansive than buying new furniture. Think about replacing your cushions if they are more than 10 years old, rounded in the front, sagging, or uncomfortable. Although it may be more expensive up front, most upholsterers recommend using high-density, fire retardant foam for durability and safety. The type of foam you choose also depends on your personal preference for firmness. Be sure also to check whether the foam is fire retardant. Most, but not all upholstery foams are. If the furniture is to be used in public, be sure to check your state's laws regarding flammability requirements for furniture.