Memory foam is a mixture of chemical compounds. It is primarily made of polyurethane with combination of other chemicals. The combination of chemicals with polyurethane varies with the manufacturers. The formulation of memory foam has been copyrighted and maintained as a trade secret by the manufacturers. This is due to the fact that different combinations of chemicals with polyurethane deliver different viscoelasticity and density of memory foam. One of the chemicals used with polyurethane is silicone additives.
The main constituent of memory foam is polyurethane. They are chemical substances with linear polymers which are made of carbamate groups (-NHCO2). These groups are called urethane, formed by the chemical reaction between a polyol and a diisocyanate. Polyol is a multiple hydroxyl group bearing alcohol and diisocyanate has two isocyanate groups. Isocyanate is a functional group with a single nitrogen, carbon and oxygen molecule. The ratio of polyol and diisocyanate used for the process is 1:2. When these compounds react with water, in the presence of catalysts like tin and amines, it forms cells which are very similar to bubbles. The size of the bubbles is controlled by surfactants, which lowers the liquid surface tension.
This reaction is an exothermic reaction and the product formed is a liquid. The liquid is then dispensed into a mold, where it expands. The expansion of the liquid is like dough and hence the liquid is called as a 'bun'. The expanded liquid dries up to form the foam or polyurethane. This polyurethane when combined with other chemicals, which are trade secrets, produces the foam of varying densities and elastic properties. After combining other chemicals with polyurethane, the mixture is allowed to dry. Then it is cut or clipped into the desirable sizes for its variety of use. The entire reaction takes about 5 minutes.
As the chemical composition of the foam is mainly polyurethane, it is combustible. If the foam gets ignited accidently, it can spread the flame rapidly and also emits toxic gases. Hence some of the manufacturers in America treat them with flame retardants like Polybrominated diphenyl ethers (PBDE). Some of the studies of PBDE have shown that they are causes for the impairment of nervous and reproductive systems in animals. Memory foam keeps away the dust mites and mildew due to its chemical composition, as these mites feed on natural fibers like cotton.
There are misconceptions that the foam contains residues of diisocyante. Diisocyanate is completely consumed in the polymerization reaction with polyol. So any product made of genuine memory foam will not contain residues of diisocyanate. There are replicas of memory foam made of cheaper constituents, which may be hazardous. Some of the manufacturers who make genuine memory foam include Tempur-Pedic, ECO-CELL, Dynamic Systems, SunMate and Pudgee.
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