A KN95 mask is a widely-used, short-length, particulate-resistant (SPF) mask, which is one of the most popular and most recommended types of masks for protecting the respiratory system of the workplace. SPF (spherical reflectance factor), also known as luminous polyethylene or PME, is an indicator of the effectiveness of a filter's ability to trap dust particles. The higher the PME level, the better the filter's ability to trap dust particles and keep them from embedding themselves in the soft t...