Japanese mesh swim caps are made of polyurethane and nylon. Fast drying, sturdy, and breathable. They are imported from Japan and run a size small. Medium caps fit like a small 20.5-21.5 inch circumference. Large caps fit like a medium 21.5-22.5inch circumference. One size Fits Most fits 20.5-23inch. Great for larger heads. They can be washed with same shampoo as your hair and left to air dry. They keep their shape. They are durable enough to withstand wig making. This cap is popular for making full wigs and u part wigs because they breath and do not lose their shape over time.