Cotton sheets are inexpensive, comfortable and machine-washable. Egyptian and Supima cotton are the softest cotton bed sheets; they're more comfortable than a polyester cotton blend because they are more breathable and absorb more moisture. The main factor when choosing cotton bed sheets is thread count, which is the number of threads in 1 square inch of fabric. Generally the higher the thread count the better, although consideration should also be given to weave. A high thread count with a weave ratio of one horizontal thread to one vertical thread, using single-ply thread, is a good formula for finding soft, comfortable cotton sheets.
Jersey king sheets made of knit cotton have plenty of stretch, meaning they have a smooth, tight fit to the mattress. Jersey sheets are a good option if you want a sightly warmer fabric than cotton. They are also machine-washable and durable.
Satin king sheets should be selected carefully. Satin sheets come either woven or knit; woven satin is smoother, softer and therefore more comfortable than knit satin. Many people assume that buying any kind of satin sheets guarantees a more comfortable sleeping surface, but knit satin sheets can often feel rougher than far cheaper cotton sheets. The main disadvantage of satin king sheets is that they are not machine-washable; they must either be hand-washed with care or dry-cleaned.
For colder climates and seasons, flannel king sheets are a practical choice. Unlike cotton, flannel is measured by weight; as a general rule, flannel sheets should weigh at least 4 ounces per square yard. Heavier flannel will feel softer and last longer.