The 3-in-1 Filter and What It Catches
Levoit's 3-in-1 cartridge stacks three stages. The pre-filter catches the big stuff, such as lint, hair and pet dander, so it doesn't clog the finer layers. The main filter traps fine airborne particles and smoke. An activated carbon layer deals with smells, smoke and fumes, which a fibrous filter can't catch because they are gases rather than particles. Carbon works by adsorption, holding gas molecules on its huge internal surface, which is why it is paired with the particle filter rather than replacing it. Levoit gives a particle retention size of 0.1 micrometers and lists cigarette and wildfire smoke, dust, pollen, pet dander and hair, odors and VOCs among what it filters. Levoit describes it as a 3-in-1 filter rather than quoting a HEPA grade. The results are easy to judge: a fresher-smelling room, less dust and a used filter visibly full of dust and hair.