A comprehensive study published in the journal Aerosol Science and Technology reports on the filtration efficiency of a variety of commercially available materials that have been used to fabricate face masks during the COVID-19 pandemic. The study was conducted last spring by the Georgia Institute of Technology amidst the global wave of PPE shortages when fabric was the most sought-after item after toilet paper. Read a list of guidelines published along with the study here.
The study considered the filtration efficiency of submicron particles of 33 different materials including single-layer woven fabrics such as cotton and woven polyester, blended fabrics, nonwoven materials, cellulose-based materials, materials commonly found and used in hospitals, and various filter materials. Researcher Nga Lee (Sally) Ng, who is an associate professor and Tanner Faculty Fellow in the School of Chemical and Biomolecular Engineering and the School of Earth and Atmospheric Sciences, speaks on the science of aerosol particles that the whole world suddenly became interested in last year:
"A submicron particle can stay in the air for hours and days, depending on the ventilation, so if you have a room that is not ventilated or poorly ventilated then these small particles can stay there for a very long period of time," said Ng. "We learned there was a lot of variability in filtration performance even in the same type of material.”
As far as filtration goes, the researchers determined that blackout drapery and sterilization wrap used for packing surgical instruments are the best commercially available options. They also concluded that masks with multiple layers are more efficient than single-layered masks.
“We found commercially available materials that provide acceptable levels of submicron particle rejection while still maintaining airflow resistance similar to a surgical mask," commented Ryan Lively, an associate professor and John H. Woody Faculty Fellow in the School of Chemical and Biomolecular Engineering. "These materials combine fabric fiber density, a maze-like structure, and fiber surface chemistry to effectively reject submicron particles."
The team reports that one person wearing a properly fitted, multilayer mask can reject up to 84% of particles expelled by the person; meanwhile, two people with such masks can reduce particle transmission by 96%. “The best way to protect ourselves and others is to reduce exhaled particles at the source, and the source is our face," Ng said. "That really gets amplified when everyone starts wearing masks. Not everyone understands the importance of airborne virus transmission, and the importance of wearing a mask. I hope that the practice will continue to help reduce the release of these viral particles into the environment and help protect others."