On 20 August 2020, a team of researchers released findings in the peer‑reviewed journal Thorax that visually compared how well various face coverings block droplets and aerosols produced while speaking, coughing and sneezing. By fitting a person with no mask, a single‑layer cloth mask, a double‑layer cloth mask and a three‑layer surgical mask, the investigators captured particle emissions with a high‑speed camera illuminated by an LED light array, revealing particles that are normally invisible to the naked eye. The footage showed that even normal speech generates a noticeable cloud of droplets.
Coughing amplified the output, and sneezing created the largest burst. Among the four conditions, the surgical mask consistently allowed the fewest particles to escape, followed by the double‑layer cloth mask.
The single‑layer cloth mask reduced droplet spread compared with no mask, but its performance lagged behind the double‑layer and surgical options. Although the authors cautioned that the visual data do not directly translate into infection risk—because that depends on the prevalence of asymptomatic or mildly symptomatic carriers—they concluded that additional fabric layers provide a stronger barrier.
Practical Guidance for Homemade Masks
During the study period, mask mandates were in force across Greater Melbourne and the Mitchell Shire, and supplies of surgical masks were limited. To help the public improve cloth‑mask efficacy, the researchers offered several construction tips: While the experiment only tested masks up to two layers, the authors referenced other work suggesting that a 12‑layer cloth mask can approach the protection level of a surgical mask and cut infection risk by roughly two‑thirds.
They acknowledged the difficulty of sewing that many layers, but emphasized that moving from one to three layers already yields a measurable benefit.
Real‑World Illustration from Missouri
The paper cited a case study from Missouri in which two hairdressers, later found to be COVID‑19 positive, continued working while wearing a mix of cloth and surgical masks. Their 139 clients also wore masks throughout the appointments.
None of the clients contracted the virus. However, one hairdresser later infected household members because masks were not worn at home. This example reinforced the notion that masks lower transmission risk when used consistently in all environments.
Implications for Public Health
The findings add to a growing body of evidence that face coverings curb the spread of SARS‑CoV‑2. The researchers noted that it remains uncertain whether masks are more valuable for source control (preventing an infected wearer from emitting virus) or for protecting uninfected wearers from inhaling aerosols; both mechanisms are likely important. In summary, the high‑speed visual data underline a clear hierarchy: surgical masks perform best, followed by multi‑layer cloth masks, with single‑layer cloth masks still offering better protection than no mask at all.
The study supports existing public‑health recommendations that encourage mask use, especially well‑fitted designs with multiple layers, as a central tool in limiting community transmission.
