In the United Kingdom, these types of pillows are called a cushion, with the word pillow used for pillows on a bed. In Spanish, a pillow is called almohada. Internally, a pillow comprises a filler made from foam, synthetic fills, feathers, or down and viscoelastic foam and latex. Traditionally straw was a filler, but this is uncomfortable and rarely used today. Feathers and down are the most expensive and usually the most comfortable; they offer the advantage of softness and their ability to conform to shapes desired by the user, more so than foam or fiber pillows.
One of the disadvantages of a down-filled pillow is that a significant number of people are allergic to them. There are currently hypoallergenic varieties of down pillows to allow people sensitive to down to enjoy the comfort of feather or down pillows. In Asia, buckwheat is a common filler, as are plastic imitations. Such pillows tend to be smaller than a standard pillow. In India, cotton is also a common filler and is considered to be healthier than synthetic fills. The fill is surrounded with a cover or shell made of cloth or silk, known as the pillow case or pillow slip. Some pillows have a fancier cover called a sham which is closed on all sides and usually has a slit in the back through which the pillow is placed.