HEPA stands for High Efficiency Particulate Accumulation. These filters clean 99, 97 % of all particles of air bigger than 3 micron. Mushroom cultivators use these filters to make a laminar flow hood. By blowing air from a ventilator through these filters it's possible to create a filter that produces air as good as sterilized. The possibility of infection becomes close to none. A laminar flow hood with a HEPA-filter is an interesting device for the experienced grower who wants to develop his mushroom cultivation. A laminar flow hood is a reasonably expensive investment, but when the mushroom growing hobby becomes out of hand, it's surely worth it.