Here in Australia, the public health advice has gradually been changing regarding the wearing of masks by the general populace.
We started with "Masks don't work, and they'll probably increase your risks of getting the virus", accompanied by pictures of health workers wearing (you guessed it) masks, and newspaper stories about the incredible shortage of masks and other PPE for health workers.
Any idiot can tell the reasoning for the message is that while masks do work for reducing spread of the virus, if everyone tries to buy them then those who need them the most (health workers) can't get them. So it makes good sense that the health authorities would lie to us here.
Now the conversation is getting a bit more honest. There's a grudging admission that masks do work, especially when worn by people who have the virus and aren't showing symptoms yet. So the advice is to make something, using multiple layers of t-shirt cotton or teatowels.
It's straightforward arithmetic. A certain percentage of people have the virus but are not showing symptoms. The public health response around people who are showing symptoms is quite good, limiting transmission. It's the asymptomatic carriers that are responsible for an increasing amount of spread. Social isolation works in general here, and widespread wearing of masks in public also helps.
In general, act in public like you have the virus. If you have the virus, the first thing you'd want to do is stick something over your face so you can't breathe droplets of it over everyone.
Being an engineer, I'm not convinced of the efficacy of a piece of woven cloth. The weaving pattern makes uniform sized holes in the weave, through which stuff is easily able to move. I've previously used non-woven poly cloth (specifically engineering wipes) as efficient filters, so a bit of google-fu revealed that this material is the secret-sauce in real facemasks.
So let's make some facemasks. They aren't going to be N95 or P2 certified, but they're going to be a whole lot more effective than something made from t-shirt fabric.
We start with the ingredients. My fabric is electrolube ECW engineering wipes, which are widely available, from for example Farnell. Each wipe makes two masks. I also use some 6mm elastic for holding it to your head, and some 1mm magnet wire for forming the nose bit.
Cut the wipe into an axe-head shape and sew two pieces together along the rounded bit of the axe head, leaving a small seam allowance.
Unfold it, seam side up, and sew the top and bottom with a more generous fold, to allow the nose wire to be inserted.
The engineering wipes make really good fabric. They don't fray, they're strong and don't tear, and are just super-amenable to sewing.
Make the nose wire from a piece of magnet wire, or really anything that you can stick in that will bend easily and retain it's shape. I whack a little loop in the end before insertion so that it doesn't poke into your face.
After pushing the magnet wire down one of the seams to the middle, the last seam goes at the ends of the mask, again leaving a generous pocket for the elastic to go through.
And tada. A non-certified, comfortable, durable, and hopefully effective mask.