This COVID19 mask uses car pollen filter material which is HEPA rated, together with a commercialy-available snorkel mask, to make a rapidly-assemblable environmental mask with great visibility. It took about 60 seconds to make. There are some exhaust ports inside where I added extra filter material which would be better for NHS/care workers. Visibility is excellent, and it stops you touching your face!
Bill of materials - mask £12 filter £4/10 = 40p, 4 tie wraps = 16p total £12:56p
For the upgrade internal filters add a few slivers of duct tape.
In the gallery I've shown some on the internal features, and where you can add internal filters especially to the front-facing exhale valve. Duct tape works well here and at the top, it adheres to plastic surfaces. For the eye->mouth valves I took them out and stuck filter material directly to the top of the valve, then reinserted it.
Kit of parts on UK eBay.
Snorkel Face Mask
Car pollen filter
£4 makes 10 filter rectangles
I didn't have long enough ones to hand so used 2x2 in series.
(Optional) Duct tape
It you want to install additional internal filters.
I went straight onto eBay and ordered a few. Right now order some separately from different sources or if from the same source wait till they post the first one then order another, to maximise the chances of one arriving, as deliveries are getting quite sporadic with the coronavirus disrupting everything. Try and get the type with the separate plug-in snorkel. If you get the type with the fold-down snorkel then you might have to saw it in half, drill out the hinge pin, or put up with the filter suck right on the end (in fact on further inspection the pin will just drift out with a hammer on a smaller pin such as a nail or drill bit). The plug-in ones will be easier to use as proper snorkel masks after all this is over!
I got hold of a car pollen filter. You could even steal one
out of your own car! Cut the material out of the cartridge using a craft knife. Cut out a rectangle of material. Enhancement: if you can get Bosch HEPA filter cartridges that will take your filtration up to N100 which is 99.97% PM3, far exceeding the N95 specification.
Fix the filter in place
Fold the material over the snorkel mounting post, making sure ALL the edges are more or less level, and fit the first tie wrap "upwind" of the edges so no air can get in unfiltered. Once you are happy fit the second tie wrap above the first. If you use re-usable tie wrap with the tang, then you can re-use them when changing the filter material. Make sure the tie wraps are nice and tight.