WHO recommends FFP2 or FFP3 (N95 or N99) for protection against COVID19 contagion via air paths.
There are a few kinds of mask to consider:
Comparing types of masks
This study compares most types of masks and shows variation in amount of particles blocked with the mask fitted on normal person. We see that respirators masks with tighter behind the ear elastic band perform slightly better compared to ear loop respirator masks (which provide less fit) and that surgical masks are providing lower protection. These results need to be weighed against real world studies. source
Pollution masks with exhaust valve
These masks were designed to provide maximum protection you while you inhale and have a valve to make exhaling easier (and release moisture). So they do not filter the air you exhale, which means they provide little protection to the people around you if you are carrying COVID19 virus.
For the general public, these masks do not stop spreading of virus in air and on shared surfaces by virus carriers so we do not recommend these types of masks.
Surgical flat masks are principally designed to filter your exhaust breathe to protect vulnerable patient from any virus you may have in your respiratory tracks. They were not designed to filter the air you breath in and in controlled tests, they only filter from 80% to 90% of particles you inhale as opposed to 95% or more of particle you exhale.
However, tests conducted in hospital show that they provide a similar protection to cup mask respirators for hospital staff. So when properly worn, surgical masks are suitable for COVID19 protection. source
Folded respirator masks
Folded respiratory masks (without valve) are suitable for COVID19 protection. They provide a high level of protection against small particle and virus, both for what you breathe in and what you breath out.
Many folded respiratory masks have ear loop and compared to masks with stronger elastic bands around the head, they may provide a few percentage less filtering and protection. But when properly adjusted, they are equivalent to other respiratory masks and may provide slightly better protection than surgical masks.
Cup shaped respirator masks
Cup shaped respiratory masks are very effective. Like folded respiratory masks, the key to their efficiency is the tight fit on the face of the user. So respiratory masks using tight behind the head elastic bands protect more than less tight ear loop elastic bands. For public use the difference is not critical and comfort and overall fit are equally important for long term adoption.
Reusable fabrics masks
Popular in France, the "mask barrière" has 3 to 4 layers of special cloth fabrics that provide above 90% filtration of small particles and can be washed 10 to 30 times. When made in France and certified by AFNOR, these masks provide public users a protection level similar to non reusable masks.
Reusable silicone masks
Some mask designs use a silicone part to fit tightly to the face and a replaceable filter part. The silicone part of the mask can be sterilized for reuse. The silicone mask provides a tight fit and lower leak rate and combined with a FFP2 or FFP3 filter, they provide higher protection with a more eco friendly filtering. These masks use as little as one third the amount of melt blown filter used in disposable masks. Our latest KM62A mask combine the advantages of reusable silicone masks with industry leading ease of breathing for long term usage.