The therm a rest synergy sheets are brushed polyester sheets that fit snuggly around all therm a rest 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