In most portable air purifiers some of the common filters are a pre-filter, carbon filter, and a HEPA filter. Most manufacturers stake a claim with regards to the quality of their air purifiers by talking about the quality of the HEPA filter. However one simple but important criteria most of them miss out divulging is the actual size of the HEPA filter material in the HEPA filter. Most all HEPA filters in portable air purifiers are of different sizes and are almost always “pleated”. The total surface area of the HEPA filter is dependent upon the depth of the pleats, the number of pleats and the overall size of the filter. The total surface area is important because it determines how long the filter will last and its capability of accumulating fine particles.
Most, if not all, of the mid to low-grade air purifiers have very shallow HEPA filters - maybe an inch or inch and a half deep at most. But some of the good air purifiers have much deeper filters. For example, the IQAir HealthPro 250 has an F8 grade filter with 2.8m2 of material and an H12/13 hyper HEPA filter with 5m2 of filter material. This is about 3-10 times of any other air purifier on the market, making it one of the most sought after machines (other than the fact that it is Swiss made and very high quality).