18. Face Mask with exhalation valve

1.  N95 respirator is the best to protect the wearer from inhaling the viruses. These should be worn by people who are immunocompromised. The effective ones are made by 3M and are "expensive" but there are non-medical N95 respirators being sold at retail stores.  

2. Cloth mask protects others from being infected, but many 3-ply ones do not have the good quality centre filter.

3. Many non-medical N95 respirators have exhalation valves to make the wear feel less stuffy as they let out unfiltered air from the wearer. This means that the asymptomatic Covid-19 wearer can still transmit the respiratory droplets to infect other. They should not be worn around other people esp. at close quarters unless the valve is covered over with tape or cloth.

They were selling at around $6.90 per respirator in Mar 2020, but much depends on the quality as some sell as cheap as $2.00.