Masks

While not featured here, I have made several dozen masks that you may have seen on my Instagram: https://instagram.com/goldknifeworks
If you have one of my masks, maintenance info is here, with thoughts on mask design and fit below:

Maintenance of my masks:

    * Mask fabric is 100% cotton and reversible
    * When properly fit (~halfway up the nose and under the chin), glasses fogging should be minimized and filtration maximized.
    * Hand or machine-wash on high, dry on regular
    * Sanitize by washing or ironing on high with steam – do not melt elastic with iron!
    * According to whitepapers, 135F for 15min should inactivate viruses, which corresponds to 15-20min in a clothes drier on regular/high
    * Elastic is not stitched in, so you can balance the tension between top and bottom, and use the cordlock to adjust elastic length
    * Elastic is easily replaced by fishing a new piece through.
    * HIGHLY recommend sanitizing after each day of use to prevent mildew from moisture or contact contamination
    * Nosewire may be flattened and squinched out for washing (unnecessary for simply drying, but recommended for machine- or hand-washing)
    * Nosewire can be flipped over for better compliance if reversing the mask

And a demo of putting it on and taking it off:
https://drive.google.com/file/d/1IzpOL0EO2FwpH86X9mCAhA1VnTlnDUIu/view?usp=sharing

Inserting nosewires into their casings on both flashy and hidden designs. They come out the same way:

On Masks in general:

Below I will detail the engineered design elements of a properly functioning cloth face mask and why they matter, so that you can evaluate the quality of masks available on the market.

There are hundreds, if not thousands, of masks available on the market from both commercial and private sellers. Most of these masks satisfy the nominal requirement of “a cloth mask that covers your nose and mouth”. However, it appears from my observations that the majority of these masks are minimally effective due to poor design and poor wearing behavior.

N95 masks are engineered to filter your breath – inhalation and/or exhalation depending on design – and tested to rigorous standard. They are surely manufactured in audited facilities and sample-tested on a regular basis. Their designs are engineered for mass manufacturing and consistency of product to meet their specs.

And before I proceed, I will point out that cloth masks pre-date modern N95’s, both in the surgical theater, and in contagion response. You can see pictures of people wearing cloth masks from the 1918 pandemic. It is a logical assumption that cloth masks CAN be effective, and the modern N95 mask is an evolution of this idea taken to a rigorous, testable conclusion.

In order for a cloth mask to mimic the behavior of an N95, at least to the limits of the fabric’s filtering ability, several design criteria MUST be met. If these criteria are not met, the mask will be FAR less effective than merely the difference between the filtering ability of meltblown filter layers and several layers of cotton fabric.

The overall goal is this: the mask must filter your breath, ideally both inhalation and exhalation. The material should be one demonstrated to be effective according to some criteria (discussed below).

Materials:
The CDC recommends two layers (three is harder to breathe through) of tightly *woven* 100% cotton. Cloth of this type has been demonstrated to effectively filter aerosolized droplets from exhalations, which are what carry virus particles. We do not exhale dry clouds of free virus particles. Woven fabrics are deemed more effective than knit fabrics (like “jersey” material) because woven fabrics stretch less, which means the gaps between fibers do not grow as much under tension. Jersey material is good for head ties, but will filter inconsistently based on how much it is stretched in practice. You can demonstrate this for yourself by looking at a light through woven and knit fabrics under tension in various directions. Natural fibers like cotton are more frizzy and friable, and likely serve to provide greater filtering area than synthetics that are made of slick plastic-like fibers. Coarse fibers like linen or wool may leave larger gaps between fibers, compromising filtering efficiency.

Fit:
Ok, so we have a rationale for current fabric selection. Is that enough? Hardly. If there are large gaps between the edges of the mask and your face, the air (both incoming and outgoing) will take the path of least resistance. The mask fabric may prevent spewn droplets from others from reaching your face directly, but you will end up with high-speed jets of air sucking in around the mask when you inhale, and blowing out under pressure when you exhale. These gaps are usually largest under the eyes and sometimes around the sides of the cheeks. Gaps under the eyes mean you would be inhaling air with potentially aerosolized droplets past your eyes in MUCH higher volume than normal. Eyes are a potential virus ingress point. This is also uncomfortable, distracting, and fogs up glasses. So fit around the nose and cheekbones/eye hollows is critical, as are the edges on the sides. While SOME air may be filtered through the mask under these loose fit conditions, most will not. The goal must be to filter as much air as possible THROUGH the fabric instead of around it.

Criteria of a mask designed for effective fit:

    1. A moldable nosewire that will hold its shape under tension.
    2. Elastics with enough tension to keep mask snug against the face under breathing conditions
    3. Adjustable tension of loops for different face sizes and geometries

How does an effective mask design solve these problems? I can offer some insight from the pattern *I* use, and other styles can be evaluated to see if they solve the problem effectively:

    1. Pleated design with fairly deep pleats ensures the sides are short – this creates a tension geometry that reduces the tendency of the nosewire to open up. It also puts a lot of fabric in front of the face while not being overly large for small faces – very versatile
    2. Around-the-head elastics with non-sewn casings so tension can be adjusted between top and bottom, and overall with a cordlock. Mask can be worn loose around neck when alone, which reduces touching and surface contamination
    3. Nosewire is replaceable, and fairly wide, offering good coverage. Doubled-up nosewire is stiffer, or a single nosewire can be used if that fits the face beter
    4. Lack of explicit shaping is more adaptable to various facial geometries
    5. Double layers of woven cotton are reasonably breathable under normal conditions

Does perfect matter?:
I argue that perfect mask fit matters, because leaving the doors standing open while you lock your windows is ineffectual security, and just lip-services (face-service?) to the practice of masking. Perfect filtering material (i.e. not ISO-rated N95 material) matters somewhat less, because anything that reduces viral ingest or exhaust will reduce the total dose of virus you receive from your environment, or the total does that you deliver to the environment. There is compelling evidence, which is consistent with long-known infectious disease science, that the size of the dose received by a victim is directly correlated with the severity of the infection. Simply put: If you get a small dose, your immune system may be able to mobilize to contain it before it replicates out of control. A large dose is more likely to replicate in your cells (remember viruses hijack your cell’s replication machinery) faster than your immune system can respond, thus overwhelming the victim. Therefore anything we do to reduce our viral dose can increase our chances of having either zero or mild illness.

How can you tell if it fits correctly/is working?:
With a pleated mask, or any mask that isn’t very rigid, you should be able to see or feel the fabric sucking in and billowing out a little bit as you breathe. This means that you are creating a pressure differential as you breathe that is filtering THROUGH the fabric instead of escaping out the sides. If you feel a breeze past your eyes, your nosewire may not be well adjusted, or elastic tension may be too light. If your glasses are fogging up, you may need to adjust your nosewire, tension, or counter-intuitively, move the mask DOWN on your nose a bit (but NOT OFF!).

How do YOU know these work?:
Good question. I have spent many many hours in my workshop wearing 3M 9210 N95 masks while forging and grinding steel, wood, and synthetics. The 3M 9210 fits me well (many other N95 masks do not). When I do not wear a mask, I blow black snot out of my nose at the end of a session. With the 9210: normal clear snot. (yay, snot!) I have now worn my own cloth masks in the shop under the same conditions, and observed exactly the same clean tissues after a session. This tells me that fit is good, and filtering is effective for the sizes of particles I am dealing with. Once fit is good, it’s up to the filtering ability of the fabric vs. the N95 material. In fact, I am now wearing my homemade masks INSTEAD of the 9210’s in my shop, since they are washable and the availability of 9210’s will be spotty for awhile.

But viruses are smaller than shop dust, right?? Shop dust comes in all sizes. I believe viruses are likely toward the smaller end, but I have no way of measuring the size ranges of my shop dust. HOWEVER: As noted above, we do not need to filter virus particles directly, but rather the microscopic water droplets that carry them. These water droplets are not single water molecules (which are smaller than viruses), but rather larger structures that hold together (I assume via surface tension of water, which you can demonstrate to yourself at a macro scale). I have also observed that my fabric mask will reduce odors from scented hand sanitizer. I googled the size of scent molecules, and while much larger than air molecules, they are still fairly small compared to the complexity of a single virus particle. In conclusion, I am confident that a well-fitting mask made of appropriate materials WILL substantially reduce the amount of virus you are likely to inhale or exhale.

And for the love of all that is holy to you, please do NOT take off your mask when you speak to people! That’s exactly the WRONG time to do so!

There are online references that I have used in developing my masks and confidence in them as a transmission mitigation tool. I may get around to adding them here. There is a lot of flaming garbage about masks on the dumpster-fire of the Internet, and there are a lot of poorly designed mask – and poorly worn masks. However, if you apply the engineering mindset to the problem at hand, consider materials, tools, and techniques, you can find your way to a sensible conclusion.

Be safe!

-Ethan