Wednesday, July 29, 2020

My mask collection

Just as different pairs of shoes are useful for different occasions, different masks are useful for different occasions. Here's my collection.

Category 1: Likely to be significantly protective

1.1. 3M 6300 half-face mask with 2091 P100 filters

Summary: Should be extremely protective for inhalation. The fit of the soft silicone and the adjustable head-straps is excellent. It is easy to breathe through thanks to the large surface area of the filters. And while the original mask has an exhalation valve, and hence doesn't protect others much, I added a 3D printed filter over the exhalation valve, loaded with surgical mask material. As a result, the mask is highly protective of the wearer and probably more protective of others than many other masks, due to the much better fit.

My use cases: Church and shopping.

Down-sides: (1) thanks to the vibrating inhalation and exhalation valves and the thick silicone, I am barely audible through this mask, so I avoid wearing it in situations where I need to communicate with someone; (2) the mask is bulky, which makes it less good for sports; (3) the filters are expensive; (4) can leak around edges on exhalation when breathing extremely hard due to strenuous physical activity.

1.2. Sonovia cloth mask with antiviral and antibacterial coating

Summary: These are the most expensive cloth masks I've seen ($53-69 each, depending on quantity). I learned about these from my mom. My first thought was that they are a scam, but as far as I can tell (but then, this is not my field) they are made by a legitimate Israeli company, backed by serious scientists (including a Nobel prize winner), and their antiviral and antibacterial copper coating apparently really does work, and lasts many cycles of washing. I got a pack of three of these (at the time, they didn't sell them individually) so my daughter could attend her (outdoor, socially distanced) high school graduation.

Unfortunately, out of the box they don't come with a nose wire, which makes the fit poor. However, it was easy to cut a seam, insert a wire and sew it closed, and now the fit is much better. They have better fit for inhalation than exhalation in my experience: if I don't adjust the straps just right, I can feel exhaled air escaping at the cheeks, but they close tight around the nose and mouth for inhalation, providing what feels like a solid seal. A nice bonus of the antiviral coating is that I do not worry about the surface of the mask being contaminated.

My use cases: When I want significant protection but also want to be able to talk, or when the 3M mask is too bulky for convenience.

Disadvantages: More difficult to breathe through than some other options, especially if drenched with sweat. When our climbing facility reopened, I climbed in this mask the first day, but when it got wet while I was climbing laps, I felt like I was drowning for lack of air.

Category 2: Likely to be moderately protective

2.1. Home-made two-layer fitted mask often paired with surgical mask

I made this from one layer of T-shirt cotton and one layer of microfiber cleaning cloth, after looking at the sizes of holes in various fabrics under a microscope. I used this pattern, enhanced with a nose wire. The fit feels superb: I don't feel the tell-tale feel of air rushing past my skin around the edges on either inhalation or exhalation. Back when I didn't have the better masks above, when I went to high risk destinations like the grocery store or church, I would sometimes put a surgical mask under it, thereby increasing the number of layers of filtration while at the same time pressing the surgical mask to my face and hence improving the surgical mask's rather terrible fit.

2.2. Ebay "KN95"

These were so cheap ($10 for ten, and I've since gotten a similar pack of ten for $5) that notwithstanding apparent Chinese certifications, I wouldn't be surprised if they were fake KN95s (and that makes me feel good about not taking protective equipment away from medical staff). However, even if they don't reach the filtration level of a real (K)N95, they fit acceptably, and I suspect--admittedly, without testing--they provide better filtration than home-made cloth options. When breathing very hard--namely, during strenuous physical activity, I can feel air rushing out by the edges of the mask at inhalation, but the mask seems to seal to the face on inhalation. Moreover, I can breathe through it even when very sweaty. I reuse these, following the advice of the N95 inventor to just have multiple masks labeled with days of the week and let them self-disinfect over the period of a week.

My use case: Indoor rock climbing.

Disadvantages:(1) suspiciously low price; (2) poor fit on exhalation

Category 3: Less likely to be moderately protective

3.1. "Surgical" mask

Summary: We have these hanging about in various places and they are convenient to toss on quickly. I can feel they leak around the edges. They are so cheap ($10 for 50 on ebay, if memory serves me) that I doubt they are serious medical protective equipment, so I feel OK about using them.

My use cases: mainly for brief contact with someone (e.g., when picking up a drive-through order in the car)

Disadvantages: Leaks around edges.

3.2. Reebok athletic mask

Summary: These are easy to breathe through, but I have no idea how much protection they provide. They are great for athletic endeavors when one is so far from people outside one's household (e.g., when playing badminton with a family member on an indoor court) that the only reason for a mask is to satisfy the rules rather than protection.

My use cases: Indoor racquet sports when alone on a court with my son. I use a better mask when closer to staff while checking into the facility.

Disadvantages: Leaks at nose bridge causing fogging in sports that require goggles (e.g., racquetball).

Category 4: Not protective

4.1. Home-made single layer T-shirt mask

Summary: I sewed these quickly from an old T-shirt and a piece of wire. Sometimes one needs a mask to satisfy rules but where realistically protection of self or others is not an issue. For instance, an outdoor facility where one can easily distance oneself from others, or while alone on an indoor court with a family member.

Use cases: I toss these in our tennis bag in case I need to go to the bathroom in my department's building after hours when I am unlikely to meet another human in the building, but the university still requires face covering. Also, outdoors at our marina.

Disadvantages: Minimal to non-existent protection of self or others.

4.2. Bandana

Summary: This provides very little protection indeed, since I can feel most of the air coming in and out around the bottom, but it does not leak much around the top and hence works well with racquetball goggles.

Use case: When I play racquetball alone in a court with a family member, the main reason to wear the face covering is to satisfy the facility rules. I am careful to wear a better mask in other areas of the building where there is closer proximity to others, such as when signing in.

Disadvantages: Minimal to non-existent protection of self and others.

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