Being in an at-risk group for COVID-19 complications, along with my wife and several of my good friends, and having some time on my hands... I'm working on a PAPR. That is a battery powered, motorized pressurized air mask. I'm using a full face snorkeling mask as the basis, although it can be easily adapted to use a standard full face filter mask or rubber respirator. The advantage over just a filter added on to the full face snorkel mask as the Czech researchers did, is you don't get "filter fatigue", it doesn't have to be specially fit, and beards and glasses are not an issue. Air enters at the top. CO2 buildup isn't much of an issue, as the air flows freely out of the purge valve at the bottom of the mask. This should also help keep them from fogging up. Make sure that whatever you get says it is silicone. Many people have a latex sensitivity, or even a full blown allergy, and may not know it yet.
This is the Smaco M8018 that I bought and am making an adapter for. https://amzn.to/34drOrh
I am designing an adapter for this, although in a pinch, PVC pipe, a heat gun, and hot glue will do. I'll be uploading my files to websites like Thingiverse when it is further along. I have an Akaso on the way, it has buckles at the bottom. I think I'll find it easier to put on. I'll design an adapter for it when it gets here. https://amzn.to/39KLZhB
Some backups. Make sure you get the L/XL if your face is 12cm or more from nose bridge to just under your chin. YMMV. https://amzn.to/2UZj9Vm https://amzn.to/39IicpB
The big rectangular HEPA 0.3 micron allergen filters (3 per pack) I ordered are no longer on the short list to be shipped, I think they ran out of what is at the local warehouse. I will include them here because they are inexpensive. https://amzn.to/2wfbF8f
A similar larger rectangular filter, quite a bit more expensive, arriving between Apr 11th and the 27th: https://amzn.to/2xSL7tQ
I was going to suggest these round filters, also HEPA 0.3 micron allergen filters for another desktop air filter. Quite a bit more expensive. Sadly, they all seem to take 10-20 days to arrive.
April 26th: https://amzn.to/2UZkqf6
Between April 11th and the 27th: https://amzn.to/39JTOnF
I think other people are having the same idea, as many of these filters were listed as taking less than a week, only a few days ago. All of these should (I'll test mine) withstand the 70C for 30 minutes recommended for killing the Corona viruses. I'm also modifying a small convection chicken roasting oven with an Arduino and thermocouple, originally for reflow soldering, but now it will also serve as a heat sterilizer for the filters. Please be cautious of DIY HEPA filters made by cutting up things like furnace filters. The 3M Filtrete HEPA furnace filters are the only ones I know that don't have fiberglass in them. Fiberglass cut up will cause tiny slivers, which will cause mesothelioma just as asbestos will. The same goes for activated charcoal, it makes tiny nanoparticles when cut that will lodge in your lungs.
McGruber! Er, I mean... MacGuyver!