18' X 40' Oval Above Ground Swimming Pool Sun Dome. This fits 18' X 40' Oval Above Ground Pools with Top Rails. This Dome comes with 1 door and 3 windows. Warming and heating is one of the key benefits - it warms the air(40 degrees) and water with solar heat up to 20 degrees Fahrenheit. It also protects your pool from leaves, bugs, debris and early spring or late summer breezes. Moreover, because your pool is protected, you cut down on the use of chemicals and expensive cleaning costs. Tailor Made Vinyl and Aluminum Enclosure The Fabrico Sun Dome is a heavy 12-gauge vinyl pool enclosure that is supported by a series of aluminum tubes. The crystal clear cover is heat-sealed to fit the tubes based on pool specifications, to provide a tailored fit for every pool size. Sturdy Double-Zipper Doors and Windows Each pool enclosure has one door opening with two heavy duty two-sided nylon zippers as well as one or more fiberglass screened window flaps/openings for flow-thru ventilation. Both doors and windows come with vinyl tabs to hold flaps in place. Solid and Secure Enclosure Framework The bottom edge of the enclosure is 24-gauge - or double thickness - and has a series of grommets. Neoprene shock cords are then attached to the grommets and hooked onto the base of the dome. This system ensures that the vinyl enclosure is held securely over the pool framework - making the Sun Dome an extra strong framework.