98%. ASTM International has an F2100 standard with similar bacterial filtering standard to the European Type II standard but in addition uses a test aerosol of 0.1 micrometre particles. The Level 3 standard F2100 standard requires that these particles must be filtered out with at least 98% efficiency. Neither the European nor the ASTM standard tests performance as worn, they just test the material — the difference being the air leakage. This is different to personal protection equipment standards such as N95 and FFP, which do test performance as worn. Surgical masks are made of a nonwoven fabric created using a melt blowing process. They came into use in the 1960s and largely replaced cloth facemasks in developed countries. The colored (usually dark blue, green, or occasionally yellow) side of the mask (fluid-repellant layer) is to be worn outwards, and the white side (absorbent layer) inwards. In some East Asian countries, masks have often customarily been worn by people who are sick in order to avoid spreading it, to protect against air pollution or allergens, as a fashion statement, or to deter social interaction. The use of surgical masks during the COVID-19 pandemic was a subject of debate, as mask shortage was a central issue. Function A surgical mask serves as a mechanical barrier that interferes with direct airflow in and out of respiratory orifices (i.e. nose and mouth). Most commonly used surgical masks are designed to only trap respiratory droplets, and therefore do not filter or block fine airborne particles that are smaller than the designed filtration ratings, which may be transmitted by coughs, sneezes, unintentional spitting during talking, or certain aerosol-generating medical procedures (e.g. bronchoscopy, laryngoscopy or dental procedures). Surgical masks also cannot provide complete protection from germs and other contaminants because of the often loose fit between the mask edges and the wearer's face, especially when the mask is worn outright incorrectly (e.g. low with the nose and/or mouth exposed). A surgical mask is a disposable device that creates a physical barrier between the respiratory tract openings (nose and mouth) of the wearer and potentially pathogenic contaminants in the immediate environment. If worn properly, surgical masks are meant to help block out most (if not all) large-particle droplets, splashes, sprays, or splatter that may contain viruses and bacteria, keeping them from entering the wearer's nose and mouth., and conversely are also effective barriers for retaining large droplets