Most masks you come across are made of melt-blown filters. These masks are thick, stuffy and technically should be replaced every few hours. This type of filter can’t be re-used, disinfected with alcohol or washed with soap. This is because melt-blown filters rely on temporal electrostatic charges to capture small particles, which can be compared to how batteries work; once they run flat they stop working and have to be thrown out. Like batteries, melt-blown filters also have a very problematic and unpredictable long term shelf-life.