Tier1 Replacement for 21x23x1 Merv 6 Basic Air Filter/Furnace Filter 6 Pack One of the most environmentally friendly filters on the market - fiberglass media is free of inks, dyes, resins, adhesives, binders, chemicals, and additives while frames use partially recycled materials, water based adhesives, and very little ink Constructed without sharp metal so they're very hand friendly - no gloves or special handling required Doesn't support microbial growth so they're a great choice where bacteria is a concern Rated UL Class 2 by Underwriters Laboratories