From bras to AC filters, scientists search for best materials to make face masks
Fabric from an old prom dress, silk, cotton bed sheets and bra cups are just a few of the items researchers have put to the test to determine which would make the best, most effective homemade face mask.
As the coronavirus spread across the U.S.,the Centers for Disease Control and Prevention asked Americans to fashion their own face masks in an effort preserve the critical protective equipment used by healthcare workers on the COVID-19 front lines.
Texas A&M professor Dr. Sarah Brooks and her team are among scientists working to determine which around-the-house mask materials actually work, local station KTRK reported. For their experiment, the group tested do-it-yourself materials against the materials used in N95 respirators to see how they stack up.
“We tried bras. We tried shower curtains. We tried coffee filters,” Brooks told the TV station in a recent interview. “A lot of people are interested in coffee filters; unfortunately they also allow a lot of passage of particles.”
The N95 masks, which are designed to fit snugly on the face and filter airborne particles, according to McClatchy News, are effective at stopping about 95 percent of nanometer particles, including the coronavirus, she explained. For Brooks and her students, the goal was to find common household materials that work just as well.
Supratik Guha, a University of Chicago professor and lead author of a study that also tested face mask materials, found that layering fabrics, such as cotton with silk or flannel, can serve as a well-functioning face covering.
“We found that many common fabrics can be surprisingly good at filtering particles,” Guha told the Boston Globe.
In the report, published in the journal NANO on April 24, researchers wrote: “We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mechanical and electrostatic-based filtration. Combining the layers to form hybrid masks ... may be an effective approach.”
The best filtration came from a mask consisting of a layer of tightly woven cotton, followed by two layers of silk or a single layer of flannel, according to the study. Two layers of chiffon also proved effective in “sandwich” of fabrics.
In their experiment, Brooks and her students found that HVAC/AC filters worked best when paired with a cloth mask. The researchers scored DIY materials on a scale of 0-100 based on their effectiveness at keeping particles out, KTRK reported.
AC filters scored 100, the best score possible. Vacuum cleaner bags scored second-best with 94, according to their findings. Brooks suggested cutting a portion of a filter or vacuum bag and sliding it into a fabric face mask.
Bandannas and coffee filters ranked among the worst performers, scoring 28 and 25, respectively.
Surgical masks received a score of 72, compared to a bra cup’s 82.
“I really thought that would be a better performer and it was even beaten by a bra,” Brooks told KTRK. “So that’s a surprise.”
Researchers warn there’s a caveat, however: how a mask is worn is just as important as the materials it’s made from. Ill-fitting coverings, such as those that gap on the sides, can “result in over a 60 percent decrease in the filtration efficiency,” according to the University of Chicago study.
“You could have the best fabric material around, but if you’re not planning to minimize those gaps, the effectiveness really drops,” Guha told The Boston Globe.
According to the CDC, face coverings should “fit snugly, but comfortably against the sides of the face,” “include multiple layers of fabric,” and “be able to be laundered and machine dried without damage or change to shape.”
This story was originally published May 1, 2020 at 4:42 PM with the headline "From bras to AC filters, scientists search for best materials to make face masks."