Pocket filters can be two- or three-ply media construction with two, three, or four pockets. A MERV 7 or MERV 8 rating is average for the 15-inch deep filters. The filters are designed to maintain the extended shape with no drooping. Self-sealing prohibits air leakage around the filter. Polyester media affords durability for handling and performance.

The deep pocket offers a massive surface area for dirt capture much like the pleated filters, except the filter is 15 inches deep instead of pleated into a 2-inch frame. This filter is used effectively as a pre-filter to enhance the life of the main filter. It can be used as the main filter to protect the unit. It is effective as the second filter in a three-filter system. One model is designed specifically for paint spray booths.

Pocket Filters Are Different Sizes and Shapes

Another design in pocket filters is a UL Class I, MERV 7 cube that is available in 8-inch, 11-inch, and 20-inch depths. The efficiency rating is from 20 to 25 percent. This compares with a three-ply media pocket filter with a MERV 8 rating and a 30 to 35 percent efficiency rating. Multi-pocket filters are available in two-ply and three-ply media at MERV 7 and MERV 8 ratings.

It is important to make sure the filter is moisture resistant and that it will hold its shape. If it sags, it will void some of the surface area for capturing pollutants. It should be self-supporting. The media should prohibit microbial growth. Make sure the operating temperature limits are within the range of the filter media.