An ER doc and his wife have another design preferable to cotton masks
Templates and instructions available in the video comments.
We don’t want to start a run on vacuum cleaner bags but if you have unused bags at home you can probably make four effective masks from each one, and maybe have an excuse to put off the vacuuming for a while…
I don’t know whether the plastic in these can survive 30 minutes of a 70⁰C oven for sterilization.