Nordic Pure 12x18x1 Pure Green AC / furnace filters are made of environmentally responsible non-woven, high loft, antimicrobial media equivalent to a MERV 8 rating. Nordic Pure’s air filter material prevents the growth of mold and bacteria. The air flow resistance with Pure Green filters is minimal, resulting in lower energy consumption, while still capturing dust, pollen, mold spores, pet dander and dust mites. The filter media is derived from recycled plastic bottles and the outer frame is beverage board made of recycled paper products. We recommend that you replace your air filter every 30-90 days.