Sheets and pillowcases are normally made of linen, cotton, or a cotton-polyester blend. (New technology, in which a cotton shell is woven around a polyester core, has significantly improved the feel of blends.) The four principal varieties of cotton, in increasing order of fineness, are American upland (90 percent of the world's cotton crop), Egyptian, pima, and sea island (the finest). Any of the four can be woven into four basic sheeting fabrics: flannel (the napped finish is wonderful for cold nights), muslin (a smooth, simple weave), oxford (soft, porous, and rather heavy; also used for shirts), or percale (finely combed and closely woven, easy to launder).

Whichever fabric type you choose, pay attention to thread count -- the number of threads per square inch. The higher the count, the finer the quality of the sheet. The highest count made in the United States is 310; 200 is a good standard.

The label on your linens may also mention finish: mercerized cotton has been treated with alkalis for a distinctive sheen; sanforized cotton has been preshrunk; easy-care and durable press finishes are mechanical or chemical treatments intended to reduce wrinkling.

American bed linens come in a standard range of sizes, with minor variations from one manufacturer to the next. (The variation is only noticeable in the depth of the "box" in a fitted sheet; better-quality sheets are deeper to accommodate the new, thicker mattresses, and need less tugging.) If you plan to choose linens outside the United States, make sure they conform to the following flat sheet sizes (don't even attempt to buy fitted sheets abroad): Twin 66" x 96"; Full 81" x 96"; Queen 90" x 102"; King 108" x 102".