BestAir 16"x27"x4" SpaceGard Pleated Air Filter. It is electrostatically charged and has a MERV 13 rating, making it effective against pollen, mold, bacteria, dust/lint, and virus carriers. This filter fits Aprilaire & SpaceGard Model 2410, 3410, 4400, & 2400/2140 and lasts up to 1 year.