There are mainly three types of activated carbon filters on the market: one used as the main filter, one with an aluminum frame, and one where carbon powder is glued directly to paper. When choosing a filter, focus on quality. A higher iodine value means better absorption of harmful gases. More tiny pores improve filtration, and lighter carbon usually means fewer impurities. Avoid filters with carbon just coated on paper—they may seem cheap, but they wear out quickly and cost more over time. Don't judge by price alone—consider performance and lifespan.