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Memory Foam: What Is It?
Memory foam is constructed from polyurethane with additional chemicals that increase its density. In technical terms, it is often referred to as visco-elastic polyurethane foam.
The foam is made up of millions of spherical shaped, open cells. What makes memory foam unique is that it is temperature and weight sensitive.
Temperature Sensitive
Being temperature sensitive, memory foam is firmer in cool temperatures (more viscous) and softer in warm temperatures (more elastic).
Higher density memory foam, such as that used in most Tempur-Pedic mattresses, is particularly temperature sensitive in that it responds to body heat by molding itself to the shape of a person's body within minutes.
This quality explains the reason people often experience a "melting" feeling when lying on higher density memory foam.
Lower density memory foam is less temperature sensitive and remains more pliable in cooler temperatures. (Learn more about higher density vs lower density.)
Weight Sensitive
Memory foam, especially higher density foam, is also weight sensitive. Unlike traditional foam that compresses and returns to its original shape right away, memory foam cells compress completely and spread their air pressure to other cells. This action allows the foam to better conform to a person's shape and, consequently, reduce pressure points.
The example often used to demonstrate the weight sensitivity of memory foam is a hand pressed into it and then removed, leaving a clear impression in the foam that slowly returns to the original shape.