SLMS window mask - draft guide/WiKi

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Based on the SSOL Smile mask

I took on the challenge to make an improved version of this in response to a request we had for a team working with young lip-readers across London

The parameters beyond simply a washable mask with a window:

  • it should be a ‘fitted’ mask, that forms a reasonable seal with the user’s face. One key feature of a fitted mask is usually a nose wire with as much breathable area as possible.

  • as much ‘breathable’ fabric area as possible. A concern with existing designs is that the window is so large that the user ends up drawing breath from the open sides of a loose fitting mask, thus circumventing any filtering qualities.

  • have an integrated filter and incorporate the latest research into materials choice. The materials chosen on reading various research papers and taking on board WHO ‘3 layer mask’ guidance

  • seal sewing machine holes in plastic window – these are seen as a potential route for infection

This is the result of trying out prototypes with some lip-readers and iterating the design

The laser cutter files are in this zip:SSOL Window mask and I’ll amend them for normal pattern cutting too

Each mask will have a piece of cotton and a piece of poly cotton cut to this pattern…

And one (in this case orange) polypropylene filter – careful with this in the laser cutter…go lightly as it melts very easily!

The polypropylene filter layer fits snugly with one of the fabric layers (you can iron the folds in advance, but the polypropylene will melt in an instant at cotton temperatures

Three layers clipped (or pinned) together ready for a stitch all round the perimeter &#8211 on this one the stitch line is engraved on the material. Pay attention to detail at this stage: accurate lining up now saves a lot of pain later

Debag by pulling everything through the middle hole, and topsew around the perimeter about 2mm from the edge

Next topsew a channel the correct width to fit an aluminium nose wire. Next: fit the wire…this is your only chance to do so!

The PETg window has been laser cut with masking tape on it: carefully remove the 5mm perimeter strip and leave the protective setion in the middle

The clear plastic (PETg) window lines up with the window in the mask body – hold it in place front and back with thin strips of masking tape (may be worth experimenting with pins as the adhesive from the tape may have caused the tread to snag?). Now comes some challenging sewing: you need to sew around the perimeter of the window very close to the fabric edge. There’s only about 5mm width of plastic under the fabric and you need to bind the ploy cotton, filter, plastic and cotton layers together with one pass. If anyone comes up with a more easily repeatable approach let me know

The masking tape tears away easily after sewing, but leave the protective piece on the window for now

All the next steps are as in the SSOL smile video (from 6:18) but I’ll add photos when I get the chance

There’s then some post processing to seal the needle holes in the window with food-safe silicone and the heatforming of the curve on the window…after which they should look something like this


This looks great.
Is there any info on how the polypro filter holds up after washing?
Edit: also have you tried one on and if so how easy is it to fog the window?

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Hard to tell. Using spunbond as opposed to melt blown, which is supposedly okay for low temperature washes, and seems fine so far – if anyone has links to specific testing/evidence base that would be great

We’re using the pp as an extra filter layer, rather than for its electrostatic properties which can be neutralised by washing I believe (the poly cotton in theory covers that)

EDIT: wore for an hour without fogging, but a smear of washing up liquid/foam soap works longer term