Our standard replaceable fluid resistant PM2.5 filter is made from non-woven spun polypropelene. It has 5 layers of filtration for the effective removal of harmful particles from the air such as pollution smog, odours, dust, pollen and other particles down to 2.5 microns. It also has an activated carbon layer to help remove odours from the air. It has filtration level of PM2.5 with an effeciency rating of 95%. It is also fluid resistant so complies to the best safety standards possible for our cotton face masks. Priced at £0.65 each or £5 for a pack of 10.