Lumbar support for back. Back wedge. Can tie it to a different types of chairs. Description from the website below: This cushion offers less thickness and firmness than the Standard Back. Features: Designed to neutralize a slightly concave or sloping back of a chair or seat, and to support the thorax or lumbar, depending upon use Can assist the body move from a constricted position and assist you to sit with more comfort and less fatigue in almost any vehicle or office seat Perfect for chairs that need just a little extra support Made in the USA Common Uses: Additional Details: 12.5" x 18" Maximum thickness of 1.5" Convenient ties to secure wedge to chair or seat Dimensionally stable fabric engineered for versatility and durability Plain poplin finish made of polyester