It's absolutely crucial that masks actually filter out very fine particulates. N95 masks are rated to filter out >=95% of 0.3 micron particles. You probably have the stock to make something close enough to a typical surgical mask, but that's not going to protect the wearer from Coronavirus, at best it would prevent a contagious patient from spreading it. You also need to form the mask such that the edges will seal against the face. I doubt you have suitable filter media on hand, and tight woven fabric will not cut it here. It's significantly harder to trap virus laden particles in the air after they've dried out, so coarse filter media is only going to be effective if it's right in front of the source where the breath is still hot and humid.
In fact, at least one study has found plain old surgical masks noninferior to N95 masks for preventing infection by flu (others have found them a little worse, and that's probably the smart way to bet). Common sense suggests that anything that prevents you from touching your mouth would help at least a little.
There is a difference between the best tool for the job and better than nothing. Our civilization has a dangerous habit of mandating the best tool for the job, and then unnecessarily suffering with nothing in an emergency.
Moreover, even if the party line that coarse unsealed masks are completely worthless at protecting the wearer from infection were true, it would still make a big difference in the rate of spread of the virus for everyone to start wearing masks! Who cares what the private benefit is when there is definitely a public benefit? And yes, we could make plenty of masks for everyone if we weren't crippled by regulation, hatred of supply and demand, and the attitude that inaction is better than imperfection.
Not OP, but here is an article that says the size-based definition of droplet vs. aerosol remains a bit vague (the article is about influenza A virus, but I believe the statement on vector size remains relevant):
"There is essential agreement that particles with an aerodynamic diameter of 5 µm or less are aerosols, whereas particles >20 µm would be large droplets. Some authors define aerosols as ≤10 µm or even ≤20 µm (Knight 1973; Treanor 2005); particles between 5 and 15 to 20 µm have also been termed ‘intermediate’ (Couch et al. 1966; all values refer to the aerodynamic diameter; for bioaerosols, they refer to the aerodynamic diameter after evaporation). When reviewing the literature, it is therefore important to verify the size of the particles being studied and the authors' definitions."
Droplet size is not generally determined by the disease. Droplet size distribution and air suspension parameters depend on humidity and temperature, as well as composition, salinity, etc.
