Filters in the ePM1 class must capture at least 50% of PM1 particles (0.3–1 μm) during testing. For example, a filter rated as ePM1 70% captures more than 70% of PM1 particles. The term ePM stands for Efficiency of Particulate Matter.

These filters effectively remove fine solid particles, ensuring healthier indoor air. They are the most efficient filters in the ISO 16890 classification.