The extra-fine fiber blend is a mixture of high-quality fabrics that are double brushed, cool, and hypoallergenic. These wonderful sheets are designed to fit oversized mattresses with extra deep pockets. This set is more durable than both cotton and sateen fibers and has a bamboo-like feel. They are also fade-resistant and wrinkle-free with no need to iron. With extremely durable elastic around the entire bottom of the fitted sheet, they are sure to fit any mattress.