If you tend to get hot when you sleep, then yes, you may want to avoid flannel sheets. But if you have your heart set on flannel, there are a couple of things you can do. First, favor cotton flannels over wool flannels and microfiber flannels (cotton tends to be more breathable than wool and synthetic materials. Then, look for a flannel with a lighter weight (5 ounces or less is ideal). If you run hot, Shaw and Moyer recommend avoiding any cheap sheets with any percentage of polyester or acrylic in the makeup. “Those are plastics,” the designers say. “Besides being unnatural, they are super sticky for the night sweats.”