It sure doesnt stop dust very well, let alone a virus.
This is the misconception that people have to understand.
The masks for everyone dont have to be able to stop a virus from getting in. They need to stop a virus from getting out!
Simple surgical masks will stop (mostly) the wearer from spreading the virus. If everyone wears one, the spread of the virus will be slowed significantly.
Everyone doesnt need an N95 mask. Only healthcare workers need these!
If everyone else can wear a simple surgical mask all the time, they will not be able to spread the virus even if they are asymptomatic and dont know they have the virus.
N95 are simply better at protecting us from any sort of airborne disease than homemade masks, which at best are only equivalent to surgical masks which only protect other people from the wearer.
Furthermore healthcare workers need better protection than N95 masks against the Wuhan Virus. The things are too uncomfortable to wear long, unuseable when doing heavy labor like turning patients over, and simply don't provide enough protection against the Wuhan Virus. They're just better than nothing. What healthcare workers need are N98 and N99 masks with better air flow and filters.
Problem is, not 1% of the public is wearing any kind of mask when out in public.
Until virtually the entire population can on a regular basis be somehow determined to be virus free, or are wearing some sort of fairly effective mask, how do the 20% of those at risk of serious illness requiring hospitalization, PLUS those in possible contact with someone in that group, not need N95 masks to avoid infection? Many in that (very large!) group are active and significant contributors to the economy.
How do we convince those who “feel ok” but might be asymptotic spreaders to “wear a mask anyway”, unless they believe there is a real threat to themselves? Ditto for the, well, “idiot” spreaders? How many people are simply not going to understand the difference? If people in this group perceive a threat to themselves sufficient to wear a mask (and this perception is NOT unjustified), they’ll demand N95 masks too.
Add all those people up and we have to be north of 1/2 of the population. That number can be whittled down a little with time.
Our health care workers are at greater risk to be sure, but, I still think we need at least a billion N95 masks a month for the next few months, to return to some semblance of safety AND economic recovery.