The Nook Pebble Full Mattress is the world’s most considered twin mattress. The Nook Pebble Twin Mattress is dual-layered with certified non-toxic foam and topped with 1” of latex foam to provide superior support and comfort. For added value and durability, the Pebble cover is removable and washable. Core Materials: Non-Toxic foam core topped with 1” of latex foam Care Instructions: Machine wash cold with mild detergent. Tumble dry. Do not use fabric softener or chlorine bleach.