Bedding, also called bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative effect, i.e. the removable and washable portion of a human sleeping environment. Multiple sets of bedding for each bed are often washed in rotation and/or changed seasonally to improve sleep comfort at varying room temperatures. Most standardized measurements for bedding are rectangular, but there are also some square-shaped sizes, which allow the user to put on bedding without having to consider its lengthwise orientation.