5-LAYER NON-WOVEN FILTRATION MATERIAL (WITH ACTIVE CARBON LAYER)
1x activated carbon
2x non-woven clothes
2x meltblown papers.
Filter size: Adults 4.5" x 3.2"
The 2.5 in PM2.5 refers to the diameter size of particles in micrometers. The symbol for micrometers also known as microns is µm and is also described in decimals as 0.001 millimeters. (As reference the diameter of the human hair is 0.1 millimetres)
Size comparison diagram shown below from the Environmental Protection Agency
Inhaling 2.5mircons particles transferred and carried through air will aggravate breathing airways, Particles this size can penetrate deep in to the lung and into the blood stream from that point.
It is recommended to change your filter twice a week if filter is used daily.