Using blue shop towels in homemade face masks can filter particles 2x to 3x better than cotton, three clothing designers discover after testing dozens of fabrics

Suay Sew Shop

A Suay employee models the blue shop towel mask

• Lindsay Medoff, CEO of Suay Sew Shop, a 30-employee boutique LA clothing manufacturer, wants the armies of people sewing homemade surgical masks to add a specific blue shop towel inside the mask.
• Medoff and two of her friends were appalled by the dozens of mask patterns in circulation today which call for cotton, a highly breathable, permeable fabric.
• They became obsessed with finding a fabric better suited for the job and built their own lab that tested particle filtration down to 0.3 microns.
• They tested every fabric they could find from coffee filters to industrial materials.
• They discovered that by adding two blue shop towels to a mask, and by using a design that produces a tighter fitting mask, their mask could block up to 95% of the particles they could test, compared to cotton masks which ranged from 20% - 60%, they found.
• These are not meant to replace the N95 masks worn by healthcare workers. The masks are designed to be an alternative to the cotton masks that many people are making and wearing for quick trips to the grocery store.
• The women are sewing 200,000 masks and giving them away for free and trying to raise money to pay their workers their full wages and giving the mask design away for free.
• They are raising money to get their mask tested with the actual COVID-19 pathogen, to see if their design for homemade masks could be validated as a safer solution to the worldwide mask shortage.
• "This is ordinary people taking their power back," Medoff said.
• Visit Business Insider's homepage for more stories.

The US boutique clothing manufacturing industry is abuzz as sewing shops retool themselves into surgical mask-making factories, like something out of a WWII "it's up to you" poster.

Lindsay Medoff, CEO and owner of 30-employee Suay Sew Shop in LA, has eagerly jumped on board. But when she got the mask-making pattern from an ER doctor friend of hers a couple of weeks ago, she was appalled.

"They sent me a pattern that looked like [it was] from Etsy," she tells Business Insider, "I thought, 'What do I do with this?'"

Suay's fashion niche is industrial "upcycling" a big fashion trend these days (the word is a play on "recycling"). The company takes unsold clothing items from major brands, such as Patagonia down vests, and re-crafts them into new clothing, recycling 85% or more of the materials.

But the mask instructions circulating on the internet are not geared to any kind of professional, industrial production. Pro shops use digital instructions, not the kind of paper patterns people buy from fabric shops like Joann's, she says.

Medoff called her best friend from high school, Chloe Schempf. Schempf also sews and previously had a career designing displays for fashion brands like Urban Outfitters and Free People. Today she's a full-time mom living in rural Michigan where her husband's veterinarian practice is located. (Her husband, Dr. Ray Harp, is a cast member on the long-running NatGeo show about country vets, The Incredible Dr. Poll.)

Schempf had dusted off her sewing machine to join the troops of homemade mask makers but when she looked at the instructions, she had another surprise.

No one seemed to be thinking about the fabric that the instructions called for: cotton and cotton fill for the filter.

How could a highly breathable cotton weave really be the right material to filter microscopic pathogen particles?

Then Schempf saw the CDC was telling healthcare workers unable to get proper gear to use a bandana as a last resort.

"The recommendation of a bandana made me ill," Schempf said. "I couldn't understand how we can go from a 2020 N95 mask to a 1918-era cotton mask with a variable filtration of 20%-60%."

Three women set up their own mask-testing shop

Clothing is all about choosing the right fabric for the right use. We don't use insulated down-filled fabric for a swimsuit or a t-shirt jersey knit for a winter coat.

So Schempf, Medoff and Medoff's business partner, Heather Pavlu, co-owner of Suay Sew Shop, became obsessed with finding a less permeable fabric for masks.

Suay Sew Shop

Suay Sew Shop CEO Lindsay Medoff testing mask particle filtration on the home made lab she and her friends built

"We spent a few days researching and brainstorming any material that could filter: coffee filters, batting, window shades, Swiffer, interfacing, etc., all the way to more technical materials that are available to specialized industrial sectors like aviation, oil refinery, medical fields," says Schempf.

Then they bought a $1,400 particulate counter device from Grainger that measures filtration ability down to 0.3 microns and spent another 10 sleepless days testing all the fabrics they could find.

They wanted a material they could buy as easily as cotton but that balanced filtration with breathability. For instance, they discovered HEPA vacuum cleaner bags had great filtration but were too suffocating to wear.

The ideal material turned out to be blue, stretchy shop towels made from a polyester hydro knit.

Inserting two of these towels into an ordinary cotton mask brought filtration up to 93% of particles as small as 0.3uM, the max their machine could test. That compared to cotton masks which filtered 60% of particles, at best, in their tests, says Schempf.

Polyester hydro knit towels are readily available at tool, hardware and automotive stores. The two brands they tested are ToolBox shop towel and ZEP's industrial blue. Interestingly, Scott Pro Shop towels, which is also made out of a hydro knit fabric didn't work as well, Schempf says.

The team is continuing to test other brands.

Harbor Freight

Tool Box Shop Towels

Having found the material, they worked on a design. "The fit has a lot to do with your protection. You can have a great mask but if you aren't getting a tight fit, it won't protect you," says Schempf.

Pavlu sewed "at least 15 types of the patterns that were being spread on the internet," she said, before the team realized they were going to have to design a new mask themselves.

So Pavlu also tracked down and rented a PortaCount Respirator Fit Tester 8040 machine and the team measured things like how a wire nose clamp helped create a high filtration, one-size-fits-all mask.

They are putting the final tweaks into their mask design and will be releasing the design for free to the public next week. The instructions will be good for home sewers and pros, available on Suay's website and their GoFundMe page.

200,000 masks from an industrial material

During their tests, they discovered another material that filtered exceptionally well: cleaning towels made from a plastic called polypropylene. They are used to clean industrial machines.

Suay Sew Shop

Suay Sew Shop's homemade fabric testing lab

Suay bought a big supply of it. But they can't recommend this fabric to the public. Open supply is dwindling, Medoff said, because the industrial makers of the material are now dedicating themselves to manufacturing medical protection supplies, she says.

Still, Suay has enough supply on hand to make 200,000 masks and have already sewn thousands, Medoff says.

They also washed this mask and retested it and discovered it held 95% of its filtration abilities after up to three machine washes.

"We are calling them semi-disposable at this point and are continuing testing after 6,7,10 washes," Pavlu said.

The next step is to test this mask, and the shop-towel version, to see if they actually block the COVID-19 pathogen, which is a smaller particle than their equipment can test.

They are curious, and hopeful about their masks, but don't have any proof these masks will protect healthy people from getting the virus any better than an ordinary cotton mask will do.

Health experts warn that surgical-style masks like these don't protect a healthy person from getting the virus but, if worn by someone who is infected, especially along with social distancing, these masks can minimize the spread that way.

Schempf found a lab in Kansas City making COVID testing kids that is willing to test their masks, she says, but the testing fee is $40,000. She's started a GoFundMe to raise the money, as well as to fund mask production efforts in her area of rural Michigan.

How masks can help

At this juncture, Medoff warns that the shop-towel masks, as well as ones from polypropylene fabric her staff are making, are not a foolproof safety measure. The logic is: if cotton masks are useful, then ones made of less permeable material can only help.

Suay is in full production giving the masks away for free to anyone who needs them.

Suay Sew Shop making thousands of their own design of surgical masks from industrial fabric

This includes medical professionals as well as nursing home workers, hospice care workers, people caring for an ill relative, and grocery store workers who are "risking their lives" on the front lines, she says.

Many of these people break down in tears when they get these masks.

Because she's paying her workers their full wages to sew the free masks, she's asking for donations via a GoFundMe.

"This is by community for community," Medoff says. "This is ordinary people taking their power back."

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