The Urban Air Valve Stopper can be used to replace your valve caps in order to reduce the exhalation function of the Urban Air Mask 2.0. Available in 3 different colors. The valve stoppers can only be used for the Urban Air Mask 2.0. The Exhalation Valve Stoppers have been tested at RISE R&D Center in Sweden with evidence showing that it will block 99% of the exhaled air, diminishing the risk of respiratory droplets escaping into the ambient air.