Three different experiments were undertaken to assess 1) shortterm protection for different types of masks worn during 10-15 minutes by the same volunteer following a standardized protocol, 2) long-term protection of a specific mask worn continuously by a volunteer for 3 hours during regular activities, and 3) effectiveness of different types of mask in preventing outgoing transmission by a simulated infectious subject. Inward protection was defined as the effect of mask wearing to protect the wearer from the environment; outward protection was defined as the effect of a mask on protecting the environment from the generation of airborne particles by a patient (or in this case a mechanical head).