Like the silhouette and the fit, the best fabric for a pair of comfy PJs will largely depend on your style and sleep temperature preferences. It's important, though, to choose a breathable, soft material that naturally regulates your body's temperature. Fabrics such as silk, linen, cotton (including Supima cotton, flannel, and jersey knits), bamboo, wool, and hemp make for some of the best sleepwear.  In general, you'll like to avoid styles entirely made from synthetics such as polyester, nylon, or rayon because they are not moisture-wicking and tend to overheat the body.