Smartline Boulder Swirl 21-Foot Round Liner | UniBead Style | 54-Inch Wall Height | 25 Gauge Virgin Vinyl | Designed for Steel Sided Above-Ground Swimming Pools 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. 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. INSTALL IN A SNAP OR A HOOK - This unibead style liner works with aboveground pools with flat-bottoms measuring 54". Unibead liners can be used on either overlap or beaded swimming pools. For use on an overlap style pool, simply open up the j-hook portion and slip this over the pool wall. For beaded style pools, use the standard bead after removing the j-hook portion along the score or groove mark. This will leave only the standard bead which is inserted into the bead receiver opening. STAY COOL IN THE POOL  Enjoy the warm weather while spending quality time with family and friends. Your backyard 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 carefree 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 25-year limited warranty is included protecting against defects in material and workmanship.