Serta Perfect Sleeper Stanberry Twin XL Firm Mattress Serta's exclusive SmartSurface with MicroSupport Gel, which combines three technologies to provide comfort and proper back support while promoting a balanced sleep temperature Cool Twist Gel Memory Foam; an exclusive liquid gel-enhanced memory foam designed to help move heat away from your body, helping to promote a balanced sleep temperature Features Serta's Free Flex Innerspring with Custom Support and Total Edge Foam Encasement The Serta Perfect Sleeper is the Only Official Mattress of the National Sleep Foundation (NSF), designed with input from the NSF to help address 5 common sleep problems. Mattress Only, Boxspring is purchased separately