2 inch Mattress TopperAdvanced Outer Cover The cover of the mattress is made of trademarked ThermaCool material. In short, this material is designed to regulate your body temperature and keep you cool during the summer months but warm during the winter months. Fiberglass Free FR Inner Cover The inner cover of the mattress provides a safe, effective flame retardant layer around our mattresses, without the negative aspects of fiberglass and other fire retardant chemicals.