Glossary
Mattress topper
A removable layer placed on top of a mattress that changes its feel and, with the right materials, how warm or cool it sleeps.
A mattress topper is a separate cushioning layer, usually a few inches thick, laid over an existing mattress rather than built into it. Because it sits directly under the sheets, its material has a large effect on how warm or cool the sleeping surface feels, sometimes more than the mattress underneath.
Toppers made from open-cell foam, latex, or fiber fill generally sleep cooler than dense memory foam, since air can move through the material instead of getting trapped against the body. Gel-infused and phase change toppers can help with initial temperature but behave the same way those materials do elsewhere in bedding, offering a short-term cooling boost rather than constant airflow.
A common mistake is buying a topper to fix a hot mattress without checking what the topper itself is made from, ending up with two heat-trapping layers stacked together. Reading the material and construction, not just the word cooling on the package, is the more reliable way to choose a topper for a hot sleeper.