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Masks, again, this time for sure. Quack.

September 4, 2021

I tried to take pictures of each step along the way.  The goal here is to make a durable, “washable” (soak in boiling water, or alcohol; I don’t think detergent is good) mask that filters very well and also breathes pretty easily, seals well, will not collapse if you breathe hard, and muffles your voice somewhat less.  I tried making one of these with no fabric, just filter material, and that is not strong enough to last; the interior layer is necessary (and feels nicer on your face).  The filter media I use here filters well — it looks good on paper, and when the west coast smoke blew into Boston, it stopped the smoke smell (it does not stop smaller smelly molecules).  For reference, from that paper, here’s the graph of filtering effectiveness and breathing resistance (which is high).  It’s the pink lines at the top, just under never-washed N95:

Mask material reuse 

The difference between this material, and medical N95, is that those use electrostatic charge, which is magically good till it wears off because you washed it (note that this chart quits at half a micron, so it is not the whole story).  Not using magic electrostatic properties means that the filtering survives exposure to alcohol, but also that the breathing resistance is much higher.  Nonetheless, I manage, most other people should as well.

The mask is shaped like a duck bill, beware, and there’s a tradeoff between area (ease of breathing) and volume (rebreathing of CO2).  The pattern itself is parameterized, so that you can adjust its size somewhat for your own personal face and your own personal preferences for ease of breathing vs rebreathing CO2 (we have varying lung sizes) vs ridiculous appearance; I put a program on the web to do this; it creates the pattern in two halves, which you print on card stock, cut out, and tape together (as seen below).  I’ll update it from time to time; notice how the pattern below printed “elastic” in the wrong place (fixed), labels one of the darts wrong, and I really wish it had a QR code that would let someone reproduce the mask without retyping parameters.

This is the 4th iteration of a design that started with one from the UF School of Anesthesiology.

Materials

  • Cummins Filtration EX 101.  This comes in packs of 50.  I can send smaller quantities to friends and family, the rest of you have your own friends and family.
  • Heat shrink tubing for capturing wire ends in the nose wire, and for holding the coffee stirrer nose brace together.
    2:1 shrink ratio, 90 degrees C activation, 1/8”, 3/16”, 1/4” (I use NTE clear from Digikey).  You can use tape for the brace joints, and if you have some other way of making a nose wire, you don’t need this.
  • 5.5” Coffee stirrers (Amazon link) for the nose brace.
  • Wire for nose wire (I use 19-gauge copper wire that I rescued from the side of the road after a lawn mower ran over a phone wire bundle).  I did once try 19-gauge stainless wire from the hardware store, it is not comfortable.
  • Cord/shoelace and cord lock for neck strap.
  • Elastic for head band.
  • Fabric — I use linen or hemp for the interior, whatever for the exterior.  Goal is both should breathe easily (the filter does the filter work), interior should be strong enough to deal with cords and braces, exterior (which is actually optional) should protect the filter from abrasion, perhaps have an appearance.  So while you can use old T-shirt for the exterior, it’s probably wrong for the interior because it is too stretchy.

Photos of steps (high-res album version):

Nose wire first.  This is 9.5 inches of copper wire, alternately use 2 pieces 4.5 and 5.5 inches long with the longer wrapped around the ends of the shorter.  To bind it all together, use heat shrink tubing, fold in a piece of fabric, then apply an iron, blast a few times with steam.  It will stick slightly to the fabric, which is why you wrap it in fabric because that is better than sticking to the iron or the ironing board.

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After doing the ends, also.

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Filter media and pattern.

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Pattern just fits the filter media, this is by design.  For the filter, don’t bother with any flaps or tabs, and don’t do the darts yet either.

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Foreshadowing: this is the ultimate destination of the nose wire.

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Pattern traced.

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Pattern cut, precisely around the face, with slop around chin and nose, to be trimmed later.

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Pattern on the interior layer, which gets all the tabs, flaps, and alignment marks for the elastic and cords.

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Traced

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Cut, again with some slop.  The flaps will fold down, and then iron to make it easier to sew.

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Exterior layer, which is a used tie-dye T-shirt.  No marking for cord attachment or tabs. Cut this with a fair amount of slop.

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And cut:

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Here’s an extra bit of more T-shirt to go inside the nose-wire flap, to help cushion the nose.

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Sewing the nose wire flap.  This is the only place where pins are appropriate, once the filter is in the mix, use clips instead because holes in the filter are to be avoided as much as possible. I have access to nice clips because my wife sews very well and my mother-in-law is a fiber artist (it was her that sent me the original pattern from UF) but bulldog clips get the job done and I have also used those.

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Sew along the bottom to leave a channel.  This will get narrower when the filter and exterior are sewed to this.

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Trim away the excess.  It doesn’t need to be super pretty, nobody will see this.  The nose wire goes inside, just shown here on the outside to show how it will be positioned.

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And with the pockets sewed.  These will also be sewed across the bottom, later.

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Recipe for stacking the layers.  This part is important, I copied it from older instructions for another pattern.  Steps will appear below.  The filter “outside” has more dimple-y dimples, bright light helps for telling them apart.

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First put the interior together, using clips to get the cords positioned right.

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Align the exterior layer on top; it’s good to get the patterns aligned for later, but this one is mostly for show, and excess will be trimmed soon.  One problem with too much extra fabric is it gets in the way of aligning the filter (one top) and the interior layer (own the bottom), which is what really matters.

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Carefully position the filter.  Goal is that its face edge (the part that curves up, around, and down from left to right) is well-aligned with the interior layer at the bottom.  Apply lots of clips to keep everything from shifting.

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One big stitch from lower left around the top to lower right.  I take my time.  It just now occurred to me, if I had no machine, could I sew this by hand, and I think the answer is “yes”.  It would be tedious, but it is entirely at the edge and I think you could whip stitch it, just fold the exterior up and on top and bind it all together.  I might start in the middle and then go to one edge, then the other.  The pockets and nose flap would be more work, but you can use more fabric there and take your time, that’s just sewing fabric.

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Use fingers to keep everything moving together, don’t want cords to shift.

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Done, from the top of the stack. (Links to high-res)

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Done, from the bottom of the stack. (Links to high-res)

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Prepare to flip interior around.

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Flipped, looking at interior and cords.

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NOW use the pattern to put the darts on the mask.  Align the pattern with the filter, which is hidden under the exterior in this photo.,

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Marked.

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I sew it somewhat more generously than the mark, probably ought to reflect that in the pattern.  Note that the clean side of the sewn dart goes against your face, for better comfort and better seal.  Design of this mask, most people won’t see the underside of your chin anyhow.

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Both darts done.

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This is the relatively tricky part and is probably subject to some further improvement.  The two chin edges need to be brought together, and then sewed.  I’ve left the pattern un-cut in the nose because there is always some imprecision here and this lets me even things up at the nose.  The clip here marks where the sewing stops.

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Finish the chin with a stitch across the darts and the center.

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After sewing the chin, need to sew the nose.  The mark on the pattern shows where.

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After sewing across the nose, clip off the excess.

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Next need to make the nose brace.  This is pretty much by eyeball, and I got the short one in the nose too long the first time.  I cut the coffee stirrers to length with some wire clippers, then use sandpaper to take off the sharp parts.

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To join the coffee stirrers together I use 1/4” heat shrink tubing.  I’ve also used gaffers tape, probably fabric adhesive tape would also work.  Again, wrap in scrap fabric and use a steam iron to shrink.

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I use two layer of heat shrink tubing — this is the completed brace.

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To fit, anchor the ends but do not fit the nose.  Put the not-in-nose angle in the chin, then push into place.  If this seems impossible, shorten as necessary.  If you need to shorten the center, either pull it apart or razor off the tubing.

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Brace in position.

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On my face. This is a lot of mask, I am trying to figure out how to fit a restraining thread through the middle of the bill to reduce its volume, that will still allow me to remove/replace the brace if I want to,  To wash this thing, take out the nose wire and brace, and either soak in boiling water or alcohol.  I tried a washing machine once, and to me it seemed to increase the breathing resistance until I washed it again in boiling water.  I’ve used one of these (not this one, but very similar design) to ride a bicycle 6 miles home from work, when we had the nasty smoke blow in from across the country.  I did not ride 100%, but I rode fast enough.  I also used a smaller one for a few hours on an airplane — it would not be adequate for exercise, but worked fine for sitting.

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