When it's time for a change - Safeguard 20-36" Replacement Window Filter Cartridge 11" Tall - Part # VC1136, replaces the expandable filter cartridge that comes in the Safeguard 11" Tall Adjustable Window Filter, Style #1136. A Safeguard window filter lets people allergic to pollen open their windows and enjoy pollen-free air. The filter keeps out dirt and dust, and is 94% efficient at trapping ragweed pollen. Coated, baffled filter slows down incoming air to increase filtration efficiency, while reducing outside noise and keeping out wind, rain and snow, all in one easy-to-change filter. Replace filter every year or when it becomes discolored due to particle collection. Package includes one (1) Safeguard 20-36" Adjustable Filter Cartridge 11" Tall.