Visco-elastic memory foam was developed from polyurethane. It is denser than polyurethane, and is also more sensitive to heat. When someone sits or lies on it, the memory foam becomes softer, allowing the person to sink into it. This way it conforms to a sitter’s or sleeper’s body contours.
The memory foam can be formulated to be more or less heat sensitive, therefore more or less conforming. When weight is removed, it “remembers” the body contour for a short time before returning to its original shape.
More information about how memory foam is made can be found on Memory Foam Mattress.Org.
About the term visco-elastic
A viscous material behaves like a thick liquid, slowly giving way to pressure. Elastic materials stretch, usually in one or few directions, then return when the stress is removed. Visco-elastic materials show both properties.
Heat and Cooling
One drawback of memory foam is its heat build-up. When it absorbs heat, it becomes warmer. For a sleeper, this can become uncomfortable. Over time, several ways have been used to cool memory foam.
The first solution was to promote air flow to make memory foam breathable. Ventilating the foam by perforation or by cutting channels in its surface allowed air to flow through it and by it.
Then manufacturers began to make the cells in the foam open and more connected to make the foam itself permeable to air. Open-cell memory foam is more breathable than closed cell foam.
Now it is common practice to infuse the memory foam with gel. The gel acts as a heat sink, carrying heat away to where it can dissipate. The most common method of gel infusion is to stir beads of microencapsulated gel into the liquid used to make the memory foam. Variations of this are the size of the beads and the kind of gel. At least one manufacturers calls its substance “gel crystals.”
Another method used by a few manufacturers is to swirl liquid gel into the memory foam mixture. This memory foam has streaks of gel. Additionally, a layer of gel itself may be embedded in the layer of memory foam. Some models use this for lumbar support.
Some manufacturers add other substances to cool the memory foam. Among these are a gel with phase change materials, diamond dust, or graphite.
Since memory foam is basically a kind of polyurethane, there may be some emissions. Using more plant-derived oils reduces this. However, memory foam has to be cut more slowly because of its “memory” and has to have time to recover before the next cut. This extra time allows the foam to air out more before being put into a mattress then packaged for shipping.
Future of memory Foam
Other materials, such as latex, have been engineered to mimic memory foam’s conformability. And microcoils are being used among the comfort layers to conform to the sleeper’s contours. Still, with new memory foam cooler than the original version, it appears that memory foam will be used in mattreses for the foreseeable future.
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