How are non-powered APR filters rated for efficiency?

Non-powered APR filters are rated for efficiency based on their ability to filter out particles of varying sizes. The efficiency of these filters is tested and rated at percentages such as 95%, 99%, and 99.7%, indicating the percentage of particles they are capable of trapping or filtering out. This rating system helps users understand the level of protection the filter can provide against different sizes of airborne particles, making it easier to choose the appropriate filter for specific pesticide application scenarios.