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.
Thread count is another important factor, but not in the way it is popularly conceived. The common knowledge about thread count is that higher is always better, but that’s not always true. In fact, brands selling sheets with astronomically high thread counts in the thousands are usually fudging the numbers with double-ply threads or other sly methods.