Post #646: Second mask liner for distribution

Posted on April 15, 2020

This white cloth above is my second and final design for a mask liner.  (The blue single-use mask is just there to show the size).

This is a piece of Filtrete 2500, encapsulated between two sheets of thin spun-bonded polyester cloth (a.k.a, floating row cover) using fusible interfacing to bind the polyester layers at the edges, then stapled to form a pleated sheet in roughly the same format as a standard surgical mask.

The idea is that you would wear this inside your tight-fitting cloth mask.  I am leaving a generous allowance of excess polyester cloth so that you can trim the edges to get the best fit to your own mask.  And so that you can find an expedient way to attach this to your own mask, in the correct position, without poking a hole in the Filtrete material.

There is no nosepiece on these.  If your cloth mask does not have a nosepiece, you should make one for it.  There are instructions for that all over the internet. You will want to position this so that the top edge of the Filtrete material is located under the metal portion of your mask nosepiece.

The pleasant surprise here is that, as constructed, this is incredibly breathable.  You pretty much don’t notice that it’s there.  (Which is, in fact, what 3M advertises about their filters.  They trap 0.3 micron particles without adding materially to the back-pressure in an HVAC system.  The MERV-13 material I have obtained, by contrast, seems to have a lot more back pressure.  So I’m going with Filtrete until I run out of it, if that ever happens.)

If , upon examination of one of these, you have any fears about inhaling a stray fiber, please attach you own thin cloth backing to the whole assembly.  This is just three pieces of non-woven polyester (or possibly polypropylene fiber).  But if the idea of breathing though this bothers you, modify it, or don’t ask for one.

If you have a mask with a filter pocket, pick out the staples and you will have a 6.75″ x 6.5″ piece of Filtrete 2500, encapsulated in spun-bonded polyester.  As long as a piece that size will do you, I don’t even have to offer something for those of you with filter pockets in your cloth masks.  Just undo the staples.

In fact, if I see little enough demand, I’ll use two pieces of Filtrete (r).  That should, in theory, capture 95% of 0.3 micron particles.  And as I said, it’s amazingly breathable, so that there seems little danger that you will breath around this, rather than through this, if you use it in a filter pocket.

For now, I’m going to advise you not to wash this material.  I know that washing N95 masks compromises there filtration ability somewhat.  I have no clue what washing does to Filtrete.  Do what hospital workers are now doing to re-use N95 masks. Drop this is a paper bag and leave it alone for a few days.  Virus particles that you may have picked up with self-destruct over time.

I need to tweak some details.  I’ll probably make this a little less wide than my single-use masks (6.75″), because I don’t want my pleats to compromise the fit of your mask.  I may also rethink the size of the pleats. But this the general idea.

The construction of these is still slow and fussy, but I’m betting I can get better at this as time moves on.  But right now, I have zero stock, and it’s going to be a while before I have a considerable supply of either of these mask liners.

If you have a mask with a tight-fitting nosepiece, this is a better option than my first mask liner.  In fact, I’m only going to offer the first one with a nosepiece, and strongly encourage people to use this design instead.  It uses less material, and it doesn’t have the cheap commercial mask material impeding the breathability of it, so, plausibly, with this design, more of your breath goes through the cloth, not around it.

In short, it’s a better design.  And, if for whatever reason, the way I’ve pleated this does not work for you, you can pick out the staples, redo it, and re-staple it.  You could probably even just tape your pleats in place.

I make no guarantees as to the effectiveness of this mask liner, if any.  I will only state that I have in fact made this out of the materials that I say I have made this from.  Most importantly, if this in any way compromises the fit of your own cloth mask, do not use it.  Minimizing air leaks is by far the most important aspect of mask use.  Better that your cloth mask filters most of your air, however it does, than that this mask liner gives you filtration that you don’t use, because it disturbs the fit of your mask.

I’m probably going to do one more variant on this that merely shapes the material into a rough conical mask, and does not have the pleats.  That would have lower risk of disturbing your cloth mask fit.  But that’s another level of difficulty.  And, frankly, I hope I am too busy making these first two designs to have the time to come up with a third.

I’m now going going to make the following offers, on some commercial platform (likely Google Forms, maybe SurveyMonkey).  I’ll set that up today and post the link here.  My offers, to Town of Vienna residents and small businesses, are the following.  You may ask for:

  • A few single-use masks, just like the blue mask in the picture above.  Trust me, when I call those cheap, it’s an insult to the word cheap.  The nosepiece, as-is, is completely inadequate, and if you use these for any purpose as stand-alone masks, you should tape a piece of wire over the embedded nosepiece and use that to shape the mask to your face.
  • A few of the white mask liner pictured above.  Unless I get feedback calling for other sizes, I’m only making one size.  It’s not difficult to make those in any size.  If you just want a piece of Filtrete, in any easy-to-handle form, for the filter pocket of your mask, order some of these.
  • A few of my first design, with nosepiece, but only for individuals who do not have a cloth mask with an adequate nosepiece.   E.g., if the only thing you’ve got is a bandana, order that one, and wear your bandana over it.
  • If I fall behind, I’ll start offering these as kits.  I’ll give you the parts, you do the pleating and the stapling.

If you don’t want to take some for free, please donate some money to some Vienna-oriented charity.  My best guess is that (e.g.) the economic situation for local small business is not going to improve any time soon.

I’ll have an order form up as soon as I can figure out how.  I’m not going to put it on this website because I realize that lot of people don’t much like what I’ve had to say, and I don’t your dislike of me to stop you from asking for one of these.  And if you know any Vienna business that still have public-facing employees (i.e., not delivery people, but anybody who has to talk to customers in person), consider pointing them to this order form.  When I figure out how to do it.

Again, I make no claims or warranties as to effectiveness.  Use at your own risk.

Christopher Hogan, Ph.D.