Which Is Better For A Sweaty Sleeper?

First, it helps to know what exactly "microfiber" even means. Microfiber sheets can be made from a variety of materials, including nylon, polyester, or even wood pulp (via Tuck). These materials are then turned into very thing fibers woven together to create a super-soft and lightweight fabric. Something that makes microfiber sheets stand out is just how thin they are; generally, they measure just 1 denier in diameter. It's that thinness that helps this type of sheet to feel so light. Microfiber is also very durable and less prone to shrinkage and wear through washing than its natural counterpart, cotton. 

Cotton, however, while it can feel a little heavier than microfiber, is still king where it comes to breathability (via Each Night). Sheets that are 100 percent cotton allow air to circulate easily, and this is true no matter the level of body heat or level of pressure applied to the sheets. In other words, even if you are really really hot on a given night and wrapped tightly in the sheets, cotton will still allow air to flow freely through the sheet, cooling you. Further, cotton is also naturally absorbent and dries quickly, so if you do sweat, the sheets will help to wick it away from you, rather than leaving you waking up slick and sticky. 

So, while microfiber can feel lighter, cotton may be the best choice for a sweaty sleeper.