Most bedding is made of either linen, cotton, or a cotton-polyester blend.  There are also four different kinds of cotton:

American Upland – a widely cultivated American cotton plant having short to medium staple fibres.

Egyptian - The world's finest cotton, it has the longest, strongest staple, resulting in the softest, most luxurious fabric and feel.

Pima - An extra long staple domestic cotton grown in the Southwest United States. The consumer identifies Pima cotton with quality.

Sea Island - cotton with especially long silky fiber.  The very finest and most expensive cotton, in very limited supply, with a fiber length greater than 1 1/2".

Cotton can also be woven into four types of sheeting fabrics:

Flannel – a plain or twill woven  cotton fabric napped and of soft yarns simulating the texture of wool flannel.  The cotton flannel must be made from cotton with a fiber long enough to hold in the yarn, otherwise the fibers will shed from the flannel or pill into little balls on the surface.

Muslin – Cloth used for sheeting with a thread count under 180 threads per inch. Muslin is more loosely woven and feels coarser than percale.

Oxford – heavier fabric

Percale – A fine, lustrous, smooth cloth with a thread count of 180 and above.

Another important thing to consider is the thread count; that is, the number of threads per square inch.  In general, the higher the thread count, the higher the quality of the sheet, and, of course, the higher the price. 

The last consideration you should make before buying your sheets is the fitted sheet size.  Because mattresses are now much higher because of the pillow-top, etc., you will need to buy “deep” sheets for this.   Deep sheets usually accommodate mattresses up to 17” or 18” high.