A bottom sheet, or fitted sheet, is the sheet with the elastic edge that fits over your mattress—hence the name bottom or fitted sheet. As today's mattresses have grown much thicker, it's important to check the measurements before buying a fitted sheet to make sure it will stretch all the way over your mattress.

However, there are lower quality cottons used in sheet making as well. Upland cotton is one of the most common. Because of its lower quality, it is often cheaper than Egyptian or Pima/Supima cotton. Additionally, organic cotton of any variety is generally more expensive than non-organic cottons.