Generally speaking, the higher the thread count, the softer and more durable the bedsheet will be. However, it's worth noting that thread count is not the only indicator of quality. Other factors, such as the type of bedsheet material used and the weaving technique, also play a role in determining the overall feel and performance of the bedsheet.
Bed sheets come in two main varieties: flat and fitted. A flat sheet is simply a rectangular sheet of cloth, while a fitted sheet has four corners, and sometimes two or four sides, fitted with elastic, to be used only as a bottom sheet. The fitted sheet may also be secured using a drawstring instead of elastic. The purpose of a fitted bottom sheet is to keep it from slipping off the mattress while the bed is in use. A particular way of folding and tucking while making the bed, known as hospital corners, is sometimes used when the bottom sheet is flat rather than fitted.
Both linen and cotton make excellent bedding fabrics and share quite a few similarities — most notably their water-absorbent qualities and that refreshing, airy feeling. But there are quite a few differences as well, and being aware of them can make it easier for you to choose between the two.