For flannel sheets, a thread count of 170-180 is considered the sweet spot for softness and warmth. Higher thread count flannel sheets may feel too heavy and trap in heat. On the other hand, cotton sheets typically have a higher thread count, with 200-800 being the standard range.

Warmer sheets, like the 225-GSM Coyuchi Cloud Brushed Flannel Sheets (best overall), will trap body heat a lot more than flannel sheets with a looser weave. If you're looking for a lighter and more breathable flannel set, consider the 135-GSM Boll & Branch Solid Flannel Sheet Set (best splurge).

Both cotton and flannel are breathable. But the napping process responsible for flannel's fuzzy texture also traps warm air. So although flannel is more loosely woven than cotton, it's also naturally warmer. Choose flannel when you want to retain warmth while you snooze and cotton if you want to sleep cooler.

In the world of flannel, the higher the ounces, the heavier—and warmer—the fabric is likely to be. The sweet spot is often considered 5 ounces per square yard, so this sheet set being 6 ounces ensures breathability without sacrificing warmth.