16″ X 25″ X 1″ Filtrete Ultra Allergen Reduction Filter from 3M – #2001 – 6 pack The Filtrete Ultra Allergen Reduction Filter carries a 3M Microparticle Performance Rating (MPR) of 1500 – roughly equivalent to a MERV 12 rating Click here for detailed comparison of 3M Filtrete 1″ Filters Features: Meets the American Lung Association Health House Indoor Air Quality Guidelines No unnecessary antimicrobial chemicals added; Filtrete filtering material will not support the growth of bacteria, mold, mildew or fungi in normal use Contains electrostatically charged media to filter and attract particles in the air 90% effective at capturing large allergens like: Pollen Mold spores   Dust mite debris Attracts and captures microscopic allergens like: Smoke Pet dander Household dust Smog Bacteria Particles that carry viruses * This filter should be changed at least every 3 months.  Certain conditions in your home will significantly add particles to the air – this will cause the filter to capture more particles, shortening it’s life to less than 3 months.  These conditions would include: dirty ductwork, pets, construction work, sanding projects, tobacco smoke, burning candles, fireplaces and wood-burning stoves. WHY USE MPR RATHER THAN MERV RATING? The  Heating, Ventilating and Air Conditioning (HVAC) industry uses the ASHRAE 52.2 Standard, which assigns a Minimum Efficiency Reporting Value (MERV) to a filter. One part of MERV reports a filter’s ability to capture medium to large particles between 1 and 10 microns. This value is helpful in comparing the performance of different filters but it is not adequate alone because particles greater than one micron make up only about 1% of the contaminants in your indoor air. Another part of MERV addresses submicron particles. 3M calls this the MPR or Microparticle Performance Rating. It measures