Up until the past couple years, standard MERV8 pre-filters, MERV14 cartridge style mid-filters, and HEPA final filters were the industry standard for indoor firing range ventilation systems. Many high volume commercial ranges were changing their pre-filters every couple weeks, their cartridge mid-filters every other month, and their HEPA filters every 9-12 months. With the introduction of the high pressure stiff pocket ‘bag’ filter, filter expenses are dropping dramatically.