Various filters for different purposes. A high-quality filter usually costs more than a cheap one. Wasting such dust protection filters seems like an expensive idea. However, in industry, the air can simultaneously contain dust, mist, and toxic gases. A pre-filter helps against these dangers. It stops solid and liquid non-volatile particles. However, toxic gases, vapors, ammonia, and similar substances pass through the filter but are stopped by the main filter. The purpose of these additional filters is to extend the lifespan of the filters in the mask. The 3M 5925 particulate filters have a P2R protection level. They are perfect for a dusty environment. They can also stop particles from water- or oil-based mists. Pre-filters are not recommended for use without other filters.