A pillowcase is a protective covering for a pillow, typically made from fabric. It serves to keep the pillow clean and hygienic while providing a comfortable surface for resting one's head. Pillowcases come in various sizes, such as standard, queen, and king, to fit different pillow dimensions. They are often designed with openings on one side for easy insertion and removal of the pillow. Pillowcases can be made from a variety of materials, including cotton, polyester, and silk. Many people choose pillowcases based on their personal preferences for softness, breathability, and ease of washing. Some pillowcases are also designed with special features, such as hypoallergenic properties or cooling technology, to enhance sleep quality.