A pleated air filter is made from a sheet of polyester, paper, or cotton folded into pleats to increase the entire surface area. This allows the filter to trap more airborne particles such as dust, dirt, and hair (from pets and humans), which could otherwise damage your furnace's blower fan and clog the AC coils. As a secondary benefit, a pleated filter will improve the indoor air quality of your home.
Pleated air filters are popular for 2 main reasons:
they are sturdier and more efficient than the conventional fiberglass filters
they cost less than the super-efficient electrostatic filters.
Pleated air filters are one of the most common filters for home heating and cooling systems.