Two layers of heavy expanded aluminum, pleated together with polyurethane foam gives 40% more surface area than a regular air filter, this permanent filter is designed to last 20+ years! Use in furnaces, air conditioners where smaller particles of dust and dirt are needed to be removed from the air. The perfect solution for eliminating the need for purchasing a new filter when it's time to change. 40% more surface area than a normal air filter, allowing the filter to capture more dust and contaminants without having to clean the filter as often as you would be replacing a throwaway filter. CONSTRUCTION - The air filter media shall consist of 20 PPI polyurethane foam, 1/8" in thickness. It shall be non-allergenic, nontoxic, with a green coloring and corrugated between .020 expanded aluminum riveted for SUPER strength. Enclosed in a .037 Aluminum Frame extra strength. The one piece frame is held together with heavy rivets at one corner. The filter shall retain 290 grams of dust per 2.25 sq ft (20x20 filter). Resistance when clean is 0.05 wg at 350 FPM air velocity. Maximum resistance at capacity is .335" w.g. A cost effective approach to filtering air, the PERMFOAM is permanent and will last for years when properly cared for. This filter will fit into any existing furnace. There is no need for expensive equipment to filter the finer particles of pollen, dust, and other contaminants that are found in the air as this filter has a higher efficiency than the throwaway filters that are available. NOTE! AS WITH MOST STANDARD FILTERS, FACE SIZE IS 1/2" LESS THAN SHOWN! This is the industry standard. FREE SUPER MICROFIBER DUSTING CLOTH INCLUDED! GREAT FOR CLEANING AND DUSTING AROUND THE HOUSE FOR A LINT, DUST AND STREAK FREE SHINE! SUPER LARGE 16X16 SQUARE WHICH IS NEARLY 2 FEET ACROSS DIAGONALLY!