4-Pack Heavy Duty 4 ft. x 8 ft. Pool Pillow for Winterizing Above Ground Pools Heavy Duty .22 MM Thick Vinyl constructed 37% heavier than industry standard. Since 1973 Robelle has been making the best products to close your pool. Use the best pool closing products designed with over 50 years of experience. Absorbs Pressure Caused By Ice Build Up Under Pool Cover Preventing Damage To Pool Walls. Pool Pillow Will Pop Before Ice Damages Pool Walls. Forces Debris From The Center Of The Pool To The Sides For Easier Cleaning Lifts Pool Cover To Prevent Water From Leeching Through Pool Cover Fill Halfway to Two-Thirds With Air to Prevent Premature Popping. If you have trouble closing the valve please use a hair dryer to loosen before closing.