Mask parameters

These parameters govern the shape of a mask that either ends in a point or in a sort of duckbill, with an option for interior bracing using coffee stirrers joined with tape or heat shrink tubing. The default fits my large face okay and has a lot of surface area, not too much volume. The shape drawn is half of the mask, designed to fit within a 200x150mm area, or half of a 200x300mm sheet of Cummins Filtration EX101 which filters very fine particles non-electrostatically, so it is durable (wash with alcohol). However, this causes it to have relatively high resistance to air flow, so more surface area is necessary for comfort -- but not so much that you rebreathe too much CO2. The filter media is reliably good and the mask seals well to my face; when smoke from the west coast blew into New England, one of these masks kept the smoke smell out, and it does not usually fog my glasses. Here are the detailed sewing instructions, with pictures.

For a small person, I would recommend trying 0.95 or 0.9 for the "cone" scale, and perhaps 0.9 for the length. For non-sedentary use, don't shrink the length. I'm able to bike at a moderate pace like that, though I don't think the resulting mask will provide enough airflow for maximum exertion. I wore a smaller mask (length-from-face 0.8, nose-to-chin 1.1, duckbill 40) for a few hours on an airplane, and it was fine. Turns out the one I wear comfortably day-to-day, including sometimes on a bicycle, is nose to-chin 1.05, length-from-face 0.9 , duckbill 30.

If a mask is too small vertically it will be annoying on your nose; if it is too large, it will come up almost to your eyes, and also leak out the sides when you exhale. To fix this, sew another dart under your chin.

To slightly improve mask performance, use a fine thread to sew a restraint in the outer part of the mask to prevent it from inflating fully when you exhale; this will reduce the amount of CO2 that you rebreathe. It's important to use a fine needle and thread so that the holes have minimum size, and want the in and out holes only a few mm apart (but more than 1mm) -- you don't want to wear a large hole in the filter media.

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This is what the two half patterns look like taped together:

Sewed into a mask:

On my face (this is "too big" above, after taking an additional dart in the chin: