Making, rather than purchasing, face masks may be a cheaper alternative during the COVID-19 pandemic, but a new study conducted by the University of Cambridge and Northwestern University has shown that certain mask materials can be dangerous if used incorrectly.
The investigation into different types of homemade mask materials found that high-efficiency particulate air (HEPA) vacuum cleaner bags were among the most effective options for filtration of airborne particles, performing at a level comparable to N95 surgical masks. Since N95 masks are often reserved for medical professionals, many home-based mask makers have improvised by inserting vacuum bags inside their cloth masks.
Use of HEPA bags comes with risks of its own, however. Wearers may unwittingly inhale harmful fibers shedding from single-use vacuum bags, especially if the bags have been cut. The research found that reusable vacuum bags are safer.
The study also revealed that many other commonly-used fabrics may shed fibers, which can impede breathing if caught in the lungs. This effect can be exacerbated when the same homemade mask is used for a prolonged period of time, as fabric can become compromised after too many washes.
When used with caution, however, homemade mask materials were found to be very effective at blocking and filtering particles that could transmit COVID-19. Using thick or layered fabric tends to improve the masks’ functionality. Another effective strategy is to sew interfacing – a textile used to stiffen or add body to fabric (think shirt collars or cuffs) – between layers.
The new study is an important step forward in informing the public on which homemade masks work, since the cost and limited supply of respirator and surgical masks leads many to seek more affordable options. Prior to the onset of the pandemic, research on mask materials and effectiveness was scarce, and early studies only tested the effectiveness of fabrics acting against particles moving at normal breathing speeds.
The Cambridge study was the first to test fabrics against higher velocity particles that would result from a human cough – speeds at which disease transmission is likely to occur. Not surprisingly, the study also found that the same fabrics that are more effective at particle filtration are often more restrictive to wearers.
The researchers suggest that further studies should be conducted to test the way that different “fits” affect mask effectiveness, as well as different particle sizes. The more information the public health community can generate on mask materials, the more effectively home manufacturers will be able to play their roles in protecting against virus transmission.