Picking a 12x30x1 means you've got a long, narrow return - common on older furnaces and certain horizontal air handler installs. The actual size of this Aerostar is 11 1/2" x 29 1/2" x 3/4", so it'll seat properly in a nominal 12x30x1 grille without forcing the frame. Three MERV grades match the filter to the household. MERV 8 for baseline dust and pollen at lowest airflow restriction. MERV 11 for households with pets, smokers, or mild allergies. MERV 13 for fine particulate filtration including smoke, bacteria, and virus-sized aerosols. Construction is electrostatic pleated synthetic media in a reinforced cardboard frame. The pleats provide the surface area; the electrostatic charge handles particles too small for the weave to catch mechanically. Manufactured in Orlando, Florida by Con-Air Industries. The pleated design means this filter outlasts flat fiberglass throwaways by a wide margin, even at higher MERV grades. Service life runs 60 to 90 days for MERV 8 and 11 in typical residential conditions, shorter for MERV 13 under heavy load. If you're replacing a fiberglass filter for the first time, expect this pleated version to feel noticeably more substantial in your hand - that's the additional media doing the work.