Here is a constantly updated index of DIY masks for various materials, tools and skills so that everybody can find a design they can build themselves. Anything is better than nothing because if everybody wears a mask, droplet emission and resulting transmission vectors are reduced. Its already working in countries that mandate mask ('face covering') use.

Yan, Jing, et al. "Modeling the Effectiveness of Respiratory Protective Devices in Reducing Influenza Outbreak." Risk Analysis 39.3 (2019): 647-661.

"...It was found that a 50% compliance in donning the device resulted in a significant...reduction in risk for fitted and unfitted N95 respirators, high‐filtration surgical masks, and both low‐filtration and high‐filtration pediatric masks. An 80% compliance rate essentially eliminated the influenza outbreak."

From this article:

Some people with swine flu travelled on a plane from New York to China, and many fellow passengers got infected. Some researchers looked at whether passengers who wore masks throughout the flight stayed healthier. The answer was very much yes… 0% of the sick passengers wore masks, compared to 47% of the healthy passengers. Another way to look at that is that 0% of mask-wearers got sick, but 35% of non-wearers did. This was a significant difference, and of obvious applicability to the current question.