Researchers Show Homemade COVID Face Masks Work – Effectiveness Varies Depending on Design

Penetration and nebulization of cough drops by single-layer homemade mask fabrics. Credit: Bal Krishan

Cotton towel cloth three-layer masks that have been shown to be the most efficient at blocking aerosolized virus.

As the spread of the virus causing COVID-19 continues, experts recommend wearing homemade face masks when surgical or N95 masks are not available to prevent the spread of the pandemic. While such makeshift masks are more economical and accessible in low-population countries, the effectiveness of cloth masks has not been studied in depth.

In Physics of Fluids, by AIP Publishing, researchers at the Indian Institute of Science studied the fate of large surrogate cough drops at varying rates, from mild to severe, while using various locally purchased substances as masks.

“Our results show that cotton towel-based fabrics were the most effective among the fabrics considered and should be sewn together as multiple layers for making homemade face masks,” said author Saptarshi Basu. “A homemade mask with three or more layers is recommended, as it can significantly suppress aerosol formation.”

The researchers analyzed the effect of washing on mask effectiveness and the results showed a negligible influence of washing on mask effectiveness up to 70 wash cycles.

Using a piezoelectric dropper dispenser, the researchers created surrogate cough drops that affected a single layer of different dust samples at different rates. The fabrics used in the study included several layers of summer stoles, handkerchief, cotton towel, and surgical masks.

The specific cotton fabric materials were selected based on their daily use and the tendency of people to cover their faces with these fabrics. The researchers used high-speed imaging to quantify the penetration threshold and amount of droplet penetration at different speeds.

The researchers looked at how dust properties, such as pore size and porosity, influence the droplet penetration through the mask.

The results are relevant to many groups, including policy makers investigating how to counteract aerosol formation by secondary nebulization of cough drops as they enter the mask fabric. For mask manufacturers and the general population, it is helpful to know that N95 and surgical masks are the most effective, but if they are not available, some specific cotton materials or homemade fabrics are suitable for effective makeshift face masks.

The findings could also be applicable in applications ranging from agriculture to medical practices, where placing a wire mesh or perhaps engineered cellulosic mesh with variable porosity can reduce the momentum of incoming spray from a nozzle, allowing optimal distribution of nutrients or pesticides to crops. is guaranteed or better disinfection in the hospital.

Reference: “Efficacy of homemade face masks against human cough: insights on penetration, nebulization and aerosolization of cough drops” by Bal Krishan, Dipendra Gupta, Gautham Vadlamudi, Shubham Sharma, Dipshikha Chakravortty and Saptarshi Basu, September 14, 2021, Physics of Fluids.
DOI: 10.1063/5.0061007