Materials and Filters

Please read this section, there is a lot of important stuff in it.


Also, it’s really important that before you use any material to make masks, make sure to wash and test it first.

If you have the time, you should read through this:

If you don’t have the time the upshot is this: Tightly woven material works better than loosely woven materials, but two layers of tightly woven is bad because it is too difficult to breathe through.

What I’m using is one layer (on the outside) of tightly woven 100% cotton, and a lining layer of 100% cotton flannel. I would also happily use nice 100% cotton t-shirt material or a 100% cotton jersey sheet for the lining.

Cotton is good because it’s tough and holds up to heat (like sterilization) and can be bleached. That said, soap kills the virus, so just throwing it in the wash will be adequate.

What I mean by tightly woven material: There is  a lot of stuff out there that will work, and some you probably already have at home. Twill, herringbone, canvas, nice sheets – the basic criteria is that if you hold it up to the light, you should be able to see light though it, but not be able to distinguish shape, so this rules out most quilting material and other lighter cotton fabrics. However, if you can’t see light through it, it probably means that it’s going to be too dense to breathe through, so that rules out a lot of denim and other types of materials used for pants and outerwear. In any event, before you start cranking out a lot of masks using whatever combo of materials you decide upon, make sure to make a sample and try it on yourself – if it is too uncomfortable or difficult to breathe though you’ll need to change it, because what’s going to happen is the worker will be forced to breathe more heavily and will start sucking in potentially contaminated air through the sides of the mask.

Filters: Potential filter materials vary. Using, reusing and cleaning these kinds of materials puts us into completely uncharted territory, so proceed with caution. Here’s what I’ve learned:

You can cut up a surgical mask to use as an additional layer of protective material between the two layers your fabric mask. Other materials that have been more or less vetted are:

Spun-bond polypropylene – which is used as weed cover and mattress covers:

Cellulose/polyester – which is used in products like clean room wipes:

In terms of cleaning these materials I have found this:

This is an excellent article with hefty references and should be read all the way through, seriously.

So, in our case of perhaps using one of these materials as an additional filter between cloth layers, it would seem like the piece of filter material should be removed before washing the mask and treated in the oven before reuse.

And please remember: tell whoever is going to be using your masks that they need to wash them before use. Even if you have washed them before delivery, they need to wash them again to completely avoid contamination.

Note: there is no guarantee that any of this will protect you from COVID-19. I’m just sharing what I’ve gleaned, and these are desperate times.

I hate that we’re here.