Synthetic 1 Inch Washable Filter This durable long-life filter is made of 100% polyester washable media that does not support microbial growth. The material does not contain an antimicrobial agent. The frame is made from sturdy rust resistant aluminum channel. It has a low pressure-drop providing optimum air flow. 80-85% Efficiency for particles of 3 to 10 microns in size. MERV 5 rated filter. Replace every 2-3 years. Vacuum or wash every 30 days. Great for use in boats and other marine applications. A perfect filter for swamp coolers and areas with high moisture. Filters-NOW does not recommend washable filters for use in home HVAC units.