Cotton sheets are described by thread count, which literally means the number of threads in the cloth. Most sheets are in the 200 range, while expensive sheets are more than 500. The higher the thread count, the softer and more durable they are. Hold up a sheet to the light to determine its quality. Light will not shine through a high-thread-count sheet. Also, high-thread-count sheets won't fuzz or pill. Another great way to test this is to scratch the sheet with your fingernail to see if any pill comes off. If so, it's a lesser-quality sheet.