A P3 filter is a type of replaceable filter designed for respiratory protective masks, such as half masks or full-face masks. The designation „P“ indicates that the filter is intended for protection against solid and liquid particles, collectively referred to as aerosols. The numeral „3“ denotes the highest protection class according to the European standard EN 143, meaning it must capture at least 99.95% of airborne particles. This type of filter provides protection against fine dust, smoke, viruses, bacteria, asbestos fibres, or radioactive particles. The P3 filter alone does not protect against gaseous substances and vapours; for this, it must be combined with a gas filter.