These pre-cut Liner Pads by LinerWorld give an extra layer of protection under your above ground pool liner. Prevent damage to your liner from roots, rocks, glass, nutgrass, and any other undergrowth that can come up from your sand base. Polyester geotextile material is impervious to almost any object. Provides heavy-duty protection from undergrowth – no more grass growing through your liner! Pre-cut to your pool size – no cutting needed. Lay on top of your sand base, under your new Liner. Replace at every liner change. Water & Mold resistant. Adds insulation to reduce heat-loss into ground. Creates a smoother floor surface. HIGHLY recommended for all above ground pools.