The Ultra pool cover is a premium solid winter cover. Solid pool covers do not allow water to pass through their material. This winter cover is intended to be used during the off-season. Please order by your pool size, as the overlap goes beyond the pool size listed. This cover includes a four-foot overlap. If you have a very large top rail, please consider a larger pool size. The Ultra winter cover features a premium scrim count (threads per square inch). The Ultra pool cover has a premium 12 x 14 scrim. Heavy-duty premium polyethylene weighs 4.5 oz./yd2. Both the scrim count and material weight are the best indicators of the overall strength and durability of your pool cover. Includes a premium quality binding around the perimeter of the cover that prevents against wear and tear, helps keep grommets in place and adds to the life expectancy of this cover. The dove grey topside of this cover is coated to prevent damage caused by the sun’s ultra-violet rays and the bottom side is black to prevent algae growth. Two premium grommets are placed on center every four feet, with these grommets, you should use the included winch and all-weather cable to secure your pool cover. For extra securing, cover clips and cover wrap (both sold separately) are suggested for pool closing. No other method of installation is recommended. The cover should be able to comfortably float on the pool water without excessive stress.