I've been searching for patterns/instructions for making a cloth mask, like ones used in asian countries for years. There are many variations out there, but I found one which allows for insertion of a replaceable filter layer. There is a youtube video which shows detailed sewing. Even though it is in Japanese, there is English on both the video text instructions, and pattern pieces. There is a downloadable pdf file for the pattern pieces on the blog page, as well as embedded youtube video:
https://blog.naver.com/autoyou11/221853586653
During corona virus outbreak, she has made the pattern free.
Also, there is a place to insert bendable wire, so that it form-fits along the bridge of the nose.
I have not made this one, but have downloaded the pattern, since we only have a few masks left.
Note: On webpage, you want to make sure that you click "translate" in your browser when it loads, so that you can read English. The video and pattern has some English text.
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Mary S.