Filter combination consisting of four specially designed individual elements arranged in sequence to reduce and eliminate various indoor air pollutants. Strong 4-stage filter: Multi-stage filtration for hygienic indoor air through pre-filter, EPA (E11) filter, and activated carbon filter with an additional cold catalyst layer. 4-in-1 combination filter made up of pre-filter, EPA (E11) filter, activated carbon filter with cold catalyst layer. Pre-filter: Coarse particle filtration for larger particles such as flakes, hair, and dust. EPA (E11 filter) made from fine fiber material: captures the smallest particles ranging from 0.1 to 3 μm (e.g., bacteria 0.6 to 1.0 μm, fine dust 0.1 – 10 μm, pollen 10 – 100 μm) for efficient air purification. Activated carbon filter: Gases and unpleasant odors. Activated carbon has excellent absorption performance - it can deodorize, dehumidify, partially bind viruses, and has a sterilizing effect. Additional cold catalyst layer: absorbs organic compounds such as formaldehyde and benzene. Eliminates 99.2% of pollutants up to a size of 3 μm from the indoor air. Consumer note: Pre-filter should be vacuumed every 1 to 2 months to remove accumulated dirt. Recommended replacement interval for the entire combination filter: at least every 12 months, depending on the usage level of the device.