I went down the internet rabbit hole trying to actually come up with the Red Cross sewing pattern for facemasks that was distributed to volunteer sewers back in 1918. Alas I have not yet come up with an actual pattern. However this is what I did find. Red Cross partnered with Butterick as well as McCalls to distribute official pattern designs for everything from trench foot slippers to Nurse’s and doctors uniforms. Pattern No. 20 for Surgical Mask and Cap weren’t for everyday man on the street wear. However the Gauze facemask from Johnson & Johnson was a much more popular option.
The closest approved instructions I could find were from the Public Health Nurse Magazine put out by the National Organization for Public Health Nursing, from the Chapter on Care of Influenza and Pneumonia Patients. The rest of the book is here on Archive.org.