Possibility of filter sterilization up to 5 times. Soak in 60% alcohol, or by 80°C temperature for 20 minutes, or by ozone, or by UV. Nanofilters capture up to 50 nanometers, while the smallest virus has 200 nanometers. Much longer lifespan, thanks to the nanomembrane and one inhaling and exhaling valve around 4 times longer than usual half masks and full face masks filters. Package contains 3 pcs.