There’s a lot of terminology thrown around in the world of cooling sheets and cooling mattresses. Temperature regulating! Airflow! Moisture wicking! Phase-change material! Most of the time, these features come back to how breathable the sheets are. Breathability means moisture can better evaporate, and “temperature-regulating” usually means the sheets are breathable enough to release the heat and moisture from your body.
What makes sheets breathable? Cotton, flax linen, and bamboo have great breathability, but not all sheets are made equally, so material alone isn’t a guarantee. Weave, as in percale’s one-over-one threads versus sateen’s three-over-one, and weight (including thread count) of the bedding comes into play. Higher thread counts are less breathable, and tighter weaves will be less breathable too. The yarn within the fabric is also important, as well as how twisted it is—a higher twist makes for a smoother, cooler feel to the fabric, while a loose twist isn’t as smooth and can trap heat.
Some companies treat sheets with something called phase-change materials, or PCMs, which are substances that absorb and release energy to either heat or cool an area. “PCMs create a microclimate,” says Karen Leonas, a professor of textile sciences at the Wilson College of Textiles at North Carolina State University. Excess body heat is absorbed by these materials and then released to the body when it’s cool.
These treatments can raise the price of cooling sheets, but they’re not super popular yet, and it’s hard to determine how well incorporated it is into the fabric. “PCMs go through thermal cyclic testing and have shown to last a long time,” Leonas says. “If this is a surface treatment, there is the possibility that some of the microcapsules will be lost due to abrasion.” Parima Ijaz, CEO of Pure Parima, agrees and says these treatments sometimes only last up to 10 washes. There are only a handful of sheets on the market that tout their use of PCMs, and our guide focuses on breathable materials and weaves rather than these treatments. It’s worth noting that PCMs will last much longer on a foam mattress, according to Leonas. If you’re still sweating at night after switching to cooling sheets, try a cooling mattress.