The Air Handler M3 Panel Filter is constructed with a premium grade, 100% polyester fiber, 3 stage media. The M3 features a dry open web on the air entering side serving as a first stage pre-filter. Smaller particles are caught by the second ply of finer denier fibers. The final layer is a tightly needled matrix treated with a non- migrating tackifier to catch and hold the smallest particles. The M3 Panel Filter is self-sealing and contains a 9-gauge internal wire frame.