Our Derby Originals Classic Horse Polar Fleece Keyhole Quarter Sheet or Exercise Rug was designed to provide a comfortable, lightweight winter riding option for riders who wish to keep their horses comfortable under saddle and help warm up and loosen up the muscles and prevent stiffness. These rugs can be worn around the saddle skirt, or over the rider's legs to help prevent chills and keep both you and your horse comfortable at the same time. Sizing Information: These quarter sheets are available in two sizes: Average Horse and Large Horse. We recommend our Average Horse size for most 14-16hh equines, and our Large Horse size for larger horses and Warmblood types between 15-17hh. Our large size is also great for average sized horses with long backs, or for riders who would like a larger keyhole through which to fit their saddle or to fit over their legs.