Great question! We’re very proud of the innovation behind our modular mattress! The Cot Bed Modular Mattress consists of 3 separate parts and 2 different sized covers. When used with our Mini Cot, the middle part is removed, the two ends join together and are secured using the smaller cover (provided). When expanding from the Mini Cot to Cot Bed, the middle part of the mattress is inserted between two ends and the larger cover is used to secure.