The Therm-a-Rest Synergy 8482 Sheets are brushed polyester sheets that fit snuggly around all Therm-a-Rest reg mattresses including tapered and rectangular designs to provide a luxurious feel plus the practicality of cleanliness and breathability while sleeping outside Integrated perimeter loops mate the sheet with our full range of quilts and blankets to create a comfortable and warm sleep system The XL size is suitable for mats up to 77 and the XXL is ideal for mats up to 80