Memory foam is a type of polyurethane foam with added chemicals. Memory foam changes its shape due to a chemical reaction triggered by trapped body heat. Proprietary formulas for memory foam vary, but the action is generally the same. Heat trapped beneath the sleeper causes the foam to conform to body shape.
There is no “natural memory foam”—this misleading claim has led to disciplinary action by the FTC. The addition of some latex, scents and hydrolyzed corn protein (MSG) to a formula does not justify the false label. MSG is made by prolonged boiling of proteins in strong acid (usually hydrochloric acid) or by fermentation.
How Memory Foam Feels
The primary attraction is initial pressure relief. It’s a novel sensation to feel memory foam contouring closely to the body. Because the reaction requires trapped heat, however, every time a sleeper changes position, the memory foam must be re-heated to fully contour again. Repeated time lags for re-contouring can cause restless sleep.
Excess heat can hamper sleep as it builds up between the sleeper’s body and the memory foam. New formulas with added cooling chemicals have been developed (similar to chemicals in gel-infused foams).
Most memory foam tends to stop responding fully after a few years, and support may become uneven. Though the surface still “springs back” visually, interior foam cells may collapse and lose their capacity to support.
Odor and Toxicity
A well-known characteristic of memory foam is its acrid smell, sometimes disguised with odor-masking chemicals. This is chemical off-gassing, and is a threat to long-term health. Headaches and respiratory problems are often reported. Odorless off-gassing continues during the life of the product, even after the smell is gone.