One surprising result was in regard to masks with valves. They found these masks to be about as effective as many two-layer home-made masks. According to Fischer, some researchers had previously thought that these masks would be highly ineffective because the valve on them is designed to make them more comfortable for the wearer and to allow their breath to escape the tight-fitting mask. In other words, they protect you from the outside world, not the other way around. The likely reason for the masks’ unexpected effectiveness in this experiment is that the valve doesn’t open unless you breathe hard, Fischer says, which means that if someone is speaking softly it may not be opening. In that case, it’s really effective. But if the valve is opening, such as if someone is talking loudly, walking fast or running, it’s ineffective because the valve is open.