Plenty of sheets are sold as cooling, but only a few of the underlying mechanisms actually do anything. Cooling comes down to two real factors: how well the fabric lets air move through it, and how quickly it moves moisture away from your skin. Everything else is mostly packaging.
Breathability is about weave and weight. An open, crisp percale weave lets warm air escape rather than trapping it against you, which is why percale cotton sleeps cooler than a dense, heavy sateen. Lighter-weight fabrics breathe more freely, too. If you run hot, a lightweight percale or a lyocell sheet will almost always beat a thick, plush set.
Moisture management is the second half. We do not just feel heat; we feel the dampness of trapped sweat. Fibers that wick moisture and dry quickly, especially eucalyptus lyocell and, to a lesser extent, bamboo viscose, keep the surface drier and therefore feel cooler through the night. This is why the best cooling sheets in our testing are typically lyocell rather than cotton.
A few claims deserve skepticism. 'Cooling' finishes and treatments tend to wash out and rarely match the effect of simply choosing a breathable fiber and weave. Phase-change marketing language sounds impressive but, in normal home conditions, the practical difference is small. Focus on fiber and weave first.
Our practical advice: if cooling is your top priority, start with eucalyptus lyocell or a lightweight percale cotton, keep the room ventilated, and skip the heavy duvet in summer. Those three choices do more than any branded cooling gimmick.