I purchased a size M, but it didn't fit, so I'm selling this item after only trying it on. The arm covers are size M, but I threw away the size M outer packaging, so they are in a size S bag. Product Description These arm covers are made of breathable polyester and provide a comfortable fit. - Product Name: ARM COVER - Size: UNISEX Medium (26-29) - Color: Black - Material: 90% Polyester, 10% Polyurethane