The unique 3 season window unit has been enjoyed by homeowners for over 35 years. This is the easiest cost effective solution to enclosing patios, porches, decks, hot tubs and more. The sliding panels fill the gap between screen enclosures and insulated 4 season rooms. The vertical units have four sliding vents that nest up or down over the attached screen. When completely open you have 75% screen. Remove the vents and you have 100% screen. Closed you have 100% protection from wind, pollen, and weather.