This Nilfisk Certified ULPA Exhaust Filter is located at the top of their Allergy Vacuums. This filter is recommended for those who have dust related allergies or asthma and desire to have the very best filtration available. It should be replaced every 5 years with typical household use. The completely sealed systems in Nilfisk Allergy Vacuums, when equipped with Certified ULPA Filters, will retain 99.999% of pollens, household dust, dust mite droppings and other allergens as small as 0.12 ?m in size. If you want outstanding filtration but don't need a filter with this degree of cleaning, consider the less expensive Nilfisk Certified HEPA exhaust filter. Both filters are tested and certified that they meet these stringent filtration specifications.