CDC homemade respiratory mask, published in the H5N1 ("bird flu") days. Not sure how much relevancy it has now, but it's interesting. Handmade and reusable.
https://diqn32j8nouaz.cloudfront.net/cdc_diy_mask.jpg
More:
https://wwwnc.cdc.gov/eid/article/12/6/05-1468-f1
https://wwwnc.cdc.gov/eid/article/12/6/05-1468_article
Previously:
https://www.homemadetools.net/forum/...371#post146495
https://www.homemadetools.net/forum/...034#post140901
https://www.homemadetools.net/forum/...328#post142264
