Coloured scanning electron micrograph (SEM) of a cross-section through an FFP3 (filtering facepiece 3) face mask. FFP is a European standard. FFP3 masks filter at least 99 percent of airborne particles. The outer layers (blue) of this mask are made from two different spunbond fabrics. The seven internal layers (white) are made from very fine meltblown fabric. The layers may be electrostatically charged so that particles adhere to them better. Spunbond and meltblown materials are both nonwoven fabric formed from fibres of thermoplastic resin, typically polypropylene, bonded by heat and or pressure. Magnification: x30 when printed at 15cm wide.