Pillow casing is usually defined as a protective cover that goes over a pillow. There are various synonyms for this term that people may use interchangeably based on personal preference or context. Pillow protector, pillow cover, pillowcase, and pillow sham are all synonymous with pillow casing. Pillow protectors are usually thicker and offer additional protection to a pillow, making it less susceptible to wear and tear. Pillowcases are typically made of cotton or linen and are a common feature in bedding sets. Pillow shams are often decorative and offer an added layer of luxury to a bed. Regardless of what term is used, the ultimate goal of a pillow casing is to keep a pillow clean and prolong its lifespan.