The Miele S142-S168 Series HEPA Filter conforms to the new stringent European standard for filtration (EN 1822) which means that it actually traps 99.99% of all particles as tiny as 0.3 of a micron. These filters are so well designed that they only need to be replaced after 50 hours of use, or approximately 12 months. There is also a convenient spot to write the date on the filter, which takes the guesswork out of when the filter should be replaced.