The filters help maintain the cleaning performance of the Dyson DC19 DC20 DC21 DC29 vacuum cleaner while reducing the infiltration of dust, pollen, and other allergens into the air you breathe. The blue 2-in-1 Dyson vacuum filter, which attaches to the rear, is made of HEPA, a highly efficient filter paper that can filter 99% of fine particles in the air, so that the air purified by the vacuum cleaner can be eliminated to reduce secondary pollution. The Dyson filter is perfect for pet owners. The Eco-Ready, anti-allergy, and Power Filtration features will keep your home clean. For best results, we recommend replacing the filter every 2-3 months for optimal performance.