The resin filter for the H2 Respire 150 hydrogen inhaler filters out any impurities in the water tank of the hydrogen inhaler. Due to more usage minerals or sediments may build up over time. The resin filter will help prevent build up of any impurities in the water tank of to keep the hydrogen inhaler working at optimal levels. This is important because you can continue enjoying high quality pure molecular hydrogen gas or Brown’s gas inhalation therapy. Each filter should be replaced 1 month or approximately 100 hours of H2 Inhalation.