Smartline Boulder Swirl 21-Foot Round Liner | Overlap Style | 48-to-52-Inch Wall Height | 20 Gauge Virgin Vinyl | Designed for Steel Sided Above-Ground Swimming Pools MEASURE TWICE, BUY ONCE  Whether installing for the first time, or replacing an existing liner, the Boulder Swirl pattern offers durability while not breaking the bank. Be sure to check the measurements of your swimming pool to assure the correct size is purchased. Pool height is determined by measuring the outside wall from the ground to underneath the top rail. Round pool size is determined by measuring from the center point wall to wall in order to obtain the diameter. PRETTY PLEASING PATTERN - Blue rocks top the swirling water backdrop with the Boulder Swirl pattern. The North American cut material is hand-folded to prevent permanent creasing and excess wrinkling. Before installing, lay the liner out in the sun for a minimum of one hour to warm up the vinyl ensuring it is able to stretch when adding water. The best temperatures to install would be between 70-80 degrees. NO TROUBLE TO INSTALL - Overlap liners are draped over the walls of the pool during the installation process. Once the bottom seam is even near the cove, the liner is ready to be secured. This material is held in place through the use of coping strips prior to putting the top rails back onto the pool. Bead receivers are not needed for this type of liner. The liner is made to work with pools which have a flat bottom and wall heights of 48 or 52. ***Will not work with Intex or Pop-Up pools*** STAY COOL IN THE POOL  Enjoy the warm weather while spending quality time with family and friends. Your backyard aboveground pool will surely become the place to be during those hot summer days. Stay cool in more ways than one with the Boulder Swirl liner. HIGH QUALITY MATERIAL - Swim care-free knowing your liner can tough it out through abrasion, chemicals and UV fading thanks to the use of Lamiclear technology. The layers are made of an acrylic top coat, a UV resistant print layer, and a 100% virgin vinyl base. This material is then welded and cut for a flawless fit and finish. A 20-year limited warranty is included protecting against defects in material and workmanship.