What is H13 True HEPA Filtration?

All Levoit True HEPA Air Purifiers have a 3-stage H13 True HEPA Filtration system. Aside from a H13 True High-Efficiency Particulate Air (HEPA) Filter, these air purifiers have an Ultra-Fine Preliminary Filter and a High-Efficiency Activated Carbon Filter that all work together seamlessly to serve different purification purposes.