The answer to this question is complex and is subject to the particular piece of memory foam we are asking about. Typical Visco memory foam mattresses can sleep hot because it holds the body heat next to your body. In some cases the manufacturer may put a 1” to 2” poly fill ticking on top to dissipate the heat. If it is of good quality and not too thick the poly fiber can work very well. If it is too thick body impressions can be a bigger issue than the sleeping hot.
Older Memory Foams need this heat from the body to soften and form to your body making them hot from the trapped heat for some people. Newer memory foam mattresses like those of the Eco Series are not temperature reactive and breathe more effectively. They feature a unique open cell structure allowing proper air flow helping the foam to dissipate heat up to 8-9 times faster than its forerunners. If you take a sample or old and new style Memory Foam and blow air through them, the new style has much less back pressure created from resistance caused by air that will not flow freely. Heat does not seem to be an issue with these new 2nd generation foams.
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