The fibers used to make the covers are made with thermoplastic polypropylene. Polypropylene is a fantastic material for outdoor use because it can endure outdoor conditions, is colorfast and moisture resistant. The covers include a well-hidden zipper. The inner cushion is made with polystyrene beads; these are breathable and make the ottoman very comfortable. We do recommend storing it indoors during the rainy season so that it is always dry when you are ready to use it. You may also spot clean the cover with a soft cloth and water or mild upholstery soap. We love the look, feel and quality of these outdoor ottomans and we think you will too. They are the perfect addition to any outdoor oasis.