Filtration Efficiency, Breathability, and Reusability of Improvised Materials for Face Masks

Abstract

There is paucity of data on the performance of different improvised materials to cope with the COVID-19 pandemic. The goal of this study is to evaluate the filtration efficiency and breathability of improvised filtration and commonly available mask materials, as well as to assess their reusability. Materials readily available to the general public such as cotton, fragrance and additive-free dry baby cleaning wipes, and those abundantly available in the hospital setting, such as sterilization wraps, were chosen for testing, amongst others. In the COVID-important 2–5 m particle range, two-layers of cotton provided filtration efficiency between 34%–66%. Amongst potential filter materials, 300-weight sterilization wraps provided approximately 80% filtration efficiency and are readily available in the healthcare setting. The addition of sterilization wrap to cotton fabrics brought the filtration efficiency to above that of the sterilization wrap (80%-90%) at the expense of added pressure drop. Four-layers of dry baby wipes performed very well with a filtration efficiency of 85% and a reasonable pressure drop (1/3 of procedure mask). Since the material is advertised as pure spunlace polypropylene and designed to contact the skin during cleaning, it would appear generally safe as a filter insert. Of improvised filters, polypropylene electrostatic HVAC filters performed the best with filtration efficiencies of >99%, but are not recommended due to the risk of confusion with glass-based HVAC filters and uncertainty regarding trace materials used in the filter. The filtration efficiency of two-layers of cotton fabrics with one-layer of sterilization wrap slightly improved over 10 laundry cycles, while the performance of other non-wovens, like dry baby wipes, degraded more rapidly and should be considered disposable. In summary, we found that a two-layer cotton fabric can provide a comfortable, breathable and reusable option. The addition of a sterilization wrap or four-layers of pure spunlace fragrance free dry baby wipes can significantly improve filtration and block expiratory aerosols at the expense of an added pressure drop.

Comprehensive characterization of protective face coverings made from household fabrics

“…The WHO has also urged the research community to actively engage in research to assess effectiveness of various interventions. This has prompted research on materials and approaches to creating face coverings from household materials, and a rapid increase in publications on material choices [ 4 – 8 ], number of layers [ 4 – 6 ], attachment mechanisms [ 1 , 9 ], performance during coughing [ 7 , 10 , 11 ], etc.…”

“…However, only a few of the filtration studies with household materials have been performed under such worst-case testing [ 5 , 6 , 23 ]. Differences in protocols across studies, [ 4 , 5 , 8 , 11 , 24 ] and widely ranging filtration efficiencies for similar materials across various labs [ 4 , 5 , 25 ] make it difficult to interpret results across studies. While surgical masks and fabrics are believed to be source controls [ 26 , 27 ], and are not intended for protecting the wearer, recently, it has been suggested that masks (surgical and face-coverings) can also protect the wearer to some extent by reducing the inoculum of the virus that results in much milder infections [ 28 ].…”

Efficient and Robust Metallic Nanowire Foams for Deep Submicrometer Particulate Filtration

“…The (0.58 ± 0.03) kPa m –1 s value measured in the 5% foam indicates high breathability, which is critical for face mask viability, as compared to that of 1.0 kPa m –1 s for the N95 respirators and 0.86 kPa m –1 s for double-layered high thread count (HTC) cotton cloth filters . For face velocities of about 0.01–0.1 m/s, PD across our foams are in the 6–60 Pa range (i.e., within the breathable range) …”

“…36 For face velocities of about 0.01−0.1 m/s, PD across our foams are in the 6−60 Pa range (i.e., within the breathable range). 37 Filtration properties of the synthesized 2ED-Cu foams have been evaluated through two tests. First, a smoke test is performed by burning small white birch wood pellets, generating smoke with PM 2.5 = 4 × 10 6 particles L −1 , PM 10 = 2.5 × 10 4 particles L −1 , and PM +10 = 1.8 × 10 3 particles L −1 , and filtering through two consecutive 5% 2ED-Cu foams.…”

A Review of the Fabrication Methods, Testing, and Performance of Face Masks

“…It has been reported that cotton is the most widely used fabric for mask and higher count cotton offer better filtering efficiency. A comparative analysis of cotton-based masks and surgical masks showed that the penetration efficiency in cotton was 97%, while that in the surgical mask was 45% [46].…”