Face masks with valves or vents do not prevent spread of the coronavirus, CDC says

The purpose of masks is to keep respiratory droplets from reaching others to aid with source control,” the agency’s guidance reads. “However, masks with one-way valves or vents allow air to be exhaled through a hole in the material, which can result in expelled respiratory droplets that can reach others. This type of mask does not prevent the person wearing the mask from transmitting COVID-19 to others.

“Therefore, CDC does not recommend using masks for source control if they have an exhalation valve or vent.”

3M, which makes valve masks for construction work, illustrates on its website how they work: inhaled air is filtered through the fabric part of the mask, and hot, humid exhaled air goes out through the valve. The system may be what you want when tearing out a kitchen for remodeling, but the valve defeats the purpose when you’re trying to slow the spread of a virus.

Public health experts recommend mask-wearing to prevent respiratory droplets from spreading into the air when you exhale, speak, cough or sneeze, and the valves allow those droplets through.

Medical masks... do not have valves.

The CDC recommends simple cloth masks instead. A few layers of cotton prevent most of the potentially infectious respiratory droplets from escaping into the air around you, and they are also much cooler than the form-fitting N95 masks. ...“reusable cloth face masks and coverings should routinely be washed depending on how often they’re worn.”