Expensive air filters are made of higher quality materials, last longer, are more efficient at trapping particles, and have a larger surface area to filter. This can improve indoor air quality and health. When it comes to furnace filters, the general rule for many HVAC professionals is “the cheaper the better.” The main function of an oven filter is to prevent large particles and debris from entering the oven, which could damage it. The most inexpensive fiberglass filters are just as capable of preventing these larger particles from entering the oven as pleated filters.
HVAC systems aren't designed to improve air quality in the home, and filters are important for heating and air conditioning to work properly. Changing your boiler filter every month is one of the most important general maintenance tasks you can do for your home's air conditioning system. Washable filters can be cleaned more often if you prefer to keep the filter spotless, in addition to not throwing the filters in the landfill every time. The cheapest filters are made of spun fiberglass, which filters air very poorly compared to materials such as paper, cotton or polyester.
More expensive air filters, such as pleated residential filters, filter out dust mites, pollen, pet dander, mold, and even bacteria, which can be worthwhile, especially for people with severe allergies. Dirty or clogged filters are never good for your system, and if you choose to use an expensive air filter instead of a cheaper one, it can be quite expensive. HEPA filters filter out bacteria and viruses, and are worthwhile for people with serious respiratory conditions, such as emphysema. You'll notice that it's much harder to breathe when you hold the oven's pleated filter against your mouth.
You'll read elsewhere that pleated filters restrict airflow, causing the furnace or air conditioning unit to work more intensively, increasing energy costs and burning the motor. If all dimensions are the same, a filter with a higher MERV rating and more folds per inch will have the same or better airflow than the same filter with a lower MERV rating and fewer folds. If you have an unusually sized filter area, some companies on the Internet are making custom filters for those unique systems. When comparing the cost of a pleated filter with a non-pleated filter, you must triple the price per filter of the non-pleated filter for an accurate comparison.