Usually a flat bed sheet is overlocked around the edges to form four seams. One of the seams is wider than the other three and helps with orienting the sheet correctly on the mattress. The wider seam goes at the head end of the mattress. Sometimes the sides do not have seams, but are finished with the selvedge only. When one makes a bed, the patterned or monogrammed side of the top sheet may be placed facing up, or facing down, in which case the top edge may be folded towards the foot of the bed to expose the design.
Decide whether you like your bedding to feel smooth and silky, cool and crisp, or cosy and warm. This will help you choose which bed linen fabric and weave will suit you best.
Commonly used in North America, but uncommon in Europe, a top sheet (also known as a flat sheet), is the sheet that separates you from your comforter, blanket, or quilt. In Europe (and very slowly catching on in the United States), the duvet cover takes the place of the top sheet.

Choosing the Right Option
However, the one aspect of fit you may want to consider is pocket depth. Fitted sheets can vary in how deep the pockets are, since mattress heights are not standardized like length and width. If your mattress is more than 10 inches tall, you may want to consider looking specifically for deep-pocket fitted sheets. We recommend the pockets be a few inches larger than the height of your bed — if your bed is 15 inches tall, look for 16 to 17 inch pockets.