The science of a perfect fit, the research around masks

Published: Feb. 25, 2021 at 9:00 PM CST
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(WSAW) - It has become the symbol of the COVID-19 pandemic. As the science evolves, so do the recommendations around wearing masks. Initially, masks were only recommended for medical personnel and symptomatic people to wear. As researchers learned COVID-19 could spread through asymptomatic people and through bioaerosols, the Centers for Disease Control and Prevention recommended in April that everyone wear one.

N95 and KN95 respirators have been identified as the most effective masks, but they have largely been reserved for medical personnel, particularly those in direct contact with COVID-19 patients, due to high demand and low supply. People took to purchasing surgical masks or making their own to at least protect others around them.

“Any covering is better than no covering at all,” Dr. John Volckens said.

He is a professor of mechanical engineering at Colorado State University. In the early stages of the pandemic, the state provided funding for him and his team to test medical-grade masks that the state was purchasing for health care workers in Colorado.

“We’ve tested, I think, thousands of masks,” he said. “We did have one donor who had the great idea of saying, look I’m going to send you a bunch of mask materials that are common for homemade mask and I want you to build every permutation and test and just report the data, which we did.”

Fit, Filtration, and Breathability

CSU tested common cloth masks made of various material to see how efficiently each one performed.
CSU tested common cloth masks made of various material to see how efficiently each one performed.(Colorado State University)

There are three factors to mask efficiency: 1) filtration, or how well the mask filters air particles, 2) breathability, or how easily can someone breathe through it, 3) fit, or how well the mask seals and fits the face.

Volckens said the SARS Co-V-2 virus all on its own is about the size of a smoke particle, 0.1 microns, but masks do not have to filter to that level.

“When a virus particle comes out of the body, it’s coated in a much larger glob of things like salt and spit and mucus,” he explained, saying in that state, the particle is much larger.

You can see the interactive data by clicking here, but the far left corner of the chart shows the best performers at the smallest particle level of about 0.5 microns.

“Some of the masks we tested have really high filtration efficiency and that’s because these masks are built with filter layers, high-quality filter layers, inside or between the cotton layers and that does make a big difference,” he stated.

Those masks being generally made with high-thread-count, 2-ply cotton with a filter layer of either melt-blown fabric, HEPA vacuum filter, or a MERV home filter. The filtration tested close to the level of N95 masks, which filter about 95% or more of the particles coming through the mask.

The worst performers were unfiltered cloth masks, bandanas, neck gaiters, and silk materials.

“When you look at it on a microscopic level, there’s a lot of gaps in that material and so small particles can easily flow through those gaps,” Volckens said.

However, those masks still can stop particles the size of pollen (or a little smaller depending upon the material), which is why Volckens said wearing something is better than nothing.

As for breathability, there are measurements for this element, but it is certainly noticeable by the wearer. Surgical masks are one of the easier materials to breathe through. Woven material like cotton can be breathable too, but if the weave is too tight then it can restrict breathing. The bigger the holes, the less filtration as well.

“You have to be able to breathe comfortably through the mask and this is why we recommend, you know, you can’t just keep adding layers to a mask because at some point it gets really too hard to breathe,” Volckens urged, adding that if you can’t breathe well, then you’ll end up taking it off or “defeating the mask” by not breathing through the material.

Then there is fit. This is also easy for the wearer to notice. If it is falling off the face in general or while talking, it is not a good fit. If glasses are fogging up, it is not a good fit.

“You could be wearing the best mask in the world, but if it has big gaps around the bridge of your nose or under your chin, air is not going to flow through the mask, it’s going to flow around the mask,” Volckens assured. “Air will always follow the path of least resistance.”

Finding the perfect fit solution

N95 and KN95 respirators are about the only masks that meet all of the standards to the level needed to protect the wearer and those around them from COVID-19, but there is barely enough supply for health care workers.

“We can’t just have a small population outfitted with the highest protection and everyone else just left to fend for themselves. In order to get out of a pandemic, everyone needs equally high protection,” Sabrina Paseman urged.

Paseman is a mechanical engineer who used to work for Apple. During the initial pandemic lockdowns, she noticed that problem, that N95 respirators worked but there were shortages around the world. She wanted to solve it in an accessible way.

“It was affecting us directly in our personal lives; my brother-in-law is an ER surgeon on the frontlines and we recognized that there was no way for us to scale the N95 respirator solution,” she said. “We started out searching the area for paint stores to see if they could sell us their extra N95 respirators, I think a whole bunch of people were trying to go with that strategy and we quickly realized that there just wasn’t enough supply.”

She, her sister Katherine Paseman, and her roommate at the time who was also a former Apple employee deconstructed an N95 mask to understand why it worked well. They learned it is made up of four layers: a soft inner liner, a fit structure, filtration material, and fluid resistant material.

They also learned surgical masks have three of those four layers. Both masks use melt-blown fabric as their filter layer, which is made up of strings of plastic layered together, much like a cotton candy machine layers sugar. The plastic also has an electrostatic charge what attracts particles. The only layer surgical masks are missing is the fit structure layer, which helps the mask seal to the face. That was the problem they looked to solve.

“I actually, like scrounged around my house because there was shelter in place at that point and I found a rubber band and I slung it over my face and I was like, oh this works pretty well,” she smiled.

This was Fix The Mask's first mask brace prototype, which is made up of three rubber bands.
This was Fix The Mask's first mask brace prototype, which is made up of three rubber bands.(Fix The Mask)

She looped three rubber bands together, creating a seal around the mouth and nose. In March of 2020 was when their nonprofit, Fix The Mask was born. They looked for the most rigorous testing methods to ensure they could create a high-quality product that would actually protect people from COVID-19. They tested the rubber band prototype and worked with the University of Iowa emergency room division of their hospital to see if the method would work well on a variety of faces. It did not fit all faces equally; those with small noses and big cheeks found it comfortable, while those with larger noses did not, but it was still a step in the right direction.

“We had some very exciting news; firstly that they tested 12 people and it passed on all of their faces with literally just a rubber band, including one person who has never been able to pass with an N95 respirator before,” Sabrina Paseman said. “So, her face was so small that the normal N95 molded masks didn’t really seal to her face properly, but this rubber band solution did.”

She had friends test it out too, but they told her it was not comfortable for long periods of time. So, their next step was to make it more comfortable. They then created a single-piece cut out of a rubber sheet. Their second version of that is available to download for free so people can create it on their own. They also make rubber material recommendations. However, this model does not fit all faces equally either and may require additional cushions like cotton balls to help assist the rubber material press firmly around the nose.

They incorporated that nose cushion into the for-sale design, the Essential Mask Brace made of biocompatible silicone.

The Essential Mask Brace incorporates nose cushions and a silicon material to seal a surgical...
The Essential Mask Brace incorporates nose cushions and a silicon material to seal a surgical mask to the face.(Fix The Mask)

They do not recommend this solution for cloth masks because their intent is to help create a high-quality product that can supplement the shortage of N95 respirators.

“When you pair the Essential Mask Brace with a melt-blown fabric mask we’re able to pass fit testing pretty easily, but when you pair the Essential Mask Brace with a cloth mask, you don’t pass fit testing in the same way,” Katherine Paseman explained.

Fix The Mask also worked with UW-Madison engineers who were working towards solving the same problem. Katherine Paseman said the university reached out to them, seeing that they were ahead of the curve and the Badgers tested out the brace, finding the same results. UWM also made its own version, the Badger Seal, which can be created using materials that cost about 50 cents. The university has a for-sale mask fitter as well as free instructions about how to make one at home.

This month, the CDC recommended the use of mask fitters and braces in the fight against COVID-19.

“Many people have said, ‘they look too silly and I’m not going to wear it,’ and I can’t disagree, they do look kind of silly, but think of it this way, one year ago today, all of us thought masks themselves looked silly and now we’re all wearing them,” Volckens said, adding that another mask can be added over the surgical mask and brace to hide it.

Double Masking

Speaking of double masking, which the CDC also recommended this month after completing research related to it, Volckens said there can be benefits to double-masking, but there should be some thought in choosing which two masks to use.

“The reason you put on a second mask is really two-fold: does it add an extra layer of filtration? That’s one good reason. And then the second reason is... if the outer mask makes a better fit, that’s a great reason to double mask because, again, you don’t want those gaps anywhere around your mask,” he said.

One reason not to double mask, he caveated, was if you cannot breathe through both of them.

Mask Research Resources

Volckens and the Pasemans have a lot of resources available about mask research.

See Colorado State University’s Mask Design 101: A bootcamp for personal face coverings during COVID-19 by clicking here for an in-depth discussion about masks.

See the Airborne Transmission of SARS-Co-V-2: A Virtual Workshop that Volckens was a part of by clicking here. This will help to explain how bioaerosol particles move in the air.

Fix The Mask continually publishes research and articles here. You can find new videos and updates on their social media platforms and on YouTube.

More research about the effectiveness of cloth masks, surgical masks, and face shields can be found here.

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