Coloured scanning electron micrograph (SEM) of pollen grains on the outer layer of a surgical face mask. The outer layers of the face mask are made from a spunbond fabric, a nonwoven fabric formed from fibres of thermoplastic resin, typically polypropylene, bonded by heat and or pressure. This type of mask filters out bacteria and viruses in liquid droplets and respiratory aerosols, but not airborne bacteria or viruses. Magnification: x200 when printed at 15cm wide.