Demonstration of a simple do-it-yourself test of mask barrier function using widely available commercial products (2025)

Abstract

By December 2020, SARS-CoV-2 caused the deaths of nearly 1.5 million people worldwide. A common strategy to mitigate spread of the virus is mask wearing. Considerable data demonstrate that masks can create an effective barrier to the respiratory droplets that can carry the virus. However, the effectiveness of consumer masks for this purpose varies, and there are currently no minimum standards that mask manufacturers must meet. Therefore, a need exists for an at-home test of mask barrier function. Here, we demonstrate a simple test to compare the function of selected masks using widely available materials and resources.

INTRODUCTION

The novel 2019 severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) emerged from Wuhan, China in December, 2019, and rapidly spread across the globe. The first travel-related cases in the United States, for example, were detected in late January 2020, and there is evidence of community spread as early as February 26^th (CDC COVID-19 Response Team, 2020). On March 11^th, the World Health Organization (WHO) declared COVID-19 a pandemic. Shortly after the WHO declaration, both the WHO and the United States Center for Disease Control and Prevention (CDC) began to recommend wearing masks in public settings. As of December 2020, statewide or regional mask mandates are in effect in 37 US states, and more than a hundred other countries have nationwide mask requirements.

Despite widespread masking, there are currently no minimum standards for mask manufacturing in the US nor any requirement for mask manufacturers to demonstrate effectiveness of their products. As a result, numerous masks made with different materials and designs are on the market, and finding one that is most effective as a barrier for containment of respiratory droplets is the responsibility of the consumer. Hence, there is an urgent need for simple, consumer-friendly, at-home tests of barrier function. Several such methods are available already, but have significant limitations. For example, the idea behind the so-called candle test is that an effective mask will prevent one from being able to blow out a candle, but it is not clear if disrupted airflow is a suitable surrogate for droplet escape as that has not been evaluated in a rigorous manner. Other approaches require specialized equipment, such as lasers combined with lenses and sophisticated computer algorithms (Fischer et al., 2020) or bacterial growth medium and incubators. These items may not be readily available outside of wet laboratories.

Herein, we describe a crude but likely effective do-it-yourself test to compare the barrier function of different masks that may enable a consumer to select the most effective one from a series of choices. The test is based on that fact that hairspray atomizers produce liquid droplets with diameters in roughly the same range as respiratory droplets. The apparatus can be assembled in minutes from widely available materials. We also provide results from our own tests with a selection of masks of differing material and construction.

METHODS AND RESULTS

We purchased UV-fluorescent hairspray, a 10 W black light with a 365 nm UV light-emitting diode (LED), a selection of test masks, and dark-colored construction paper (“target paper”) from an online retailer. Similar products are available through multiple online retailers, as well as brick-and-mortar hobby stores. We then modified a long rectangular cardboard box by cutting slots in the sides to hold the target paper and masks approximately 0.5” apart (Fig. 1A). To ensure the masks are held firmly in place and stretched similar to regular use, we cut flaps along the sides of the box to accommodate the ear loops and pulled the loops tight. Next, we cut a channel in the bottom of the box to allow entry of the top of the hairspray canister. The channel stopped approximately 1.5” back from the mask. We chose to leave a space between the canister and mask to minimize artifactual passage of liquid through the mask due to the high pressure of the liquid stream upon exit from the cannister nozzle. This also ensures that liquid droplets can spread out to avoid saturating the mask in one spot in case that reduces barrier effectiveness. To test the barrier function of a mask, the user simply places the mask and target paper in their respective slots, inserts the canister, briefly sprays the paper through the mask, and then views the target paper under the black light. As we have done in our tests, we recommend including a positive control mask (such as a common surgical mask) and/or negative control (such as a thin neck gaiter) for comparison. If a consumer mask prevents passage of the hairspray as well as the surgical-style mask, then the consumer mask may be considered an effective barrier in this test.

To demonstrate use of the apparatus, we tested four common types of mask of variable construction: 1) A single-layer cotton neck gaiter, 2) a single layer cotton mask, 3) a two-layer cotton mask, and 4) a three-layer surgical style mask with filter. The results are presented in Fig. 1B. It is clear from the images that the neck gaiter was least effective in blocking the hairspray droplets. The single layer cotton mask was more effective than the neck gaiter, while results for the two-layer cotton mask and the surgical-style mask were similar. Importantly, these results are consistent with controversial preliminary data indicating that neck gaiters are poor droplet barriers (Fischer et al., 2020) and, combined with the data showing greatest droplet reduction with the positive control surgical-style mask, help to validate the test method.

DISCUSSION

Masks are intended to protect the people around us in case we are carrying an infectious respiratory illness. Although we believe the method to test barrier function presented here may be useful, it is important to understand that any convenient at-home test of mask function is likely to be crude given the limited experimental sophistication that is possible for the average consumer. Ours is no exception. For one thing, the physicochemical properties and aerosol behavior of propellant-driven hairspray droplets almost certainly differ significantly from those of respiratory droplets produced by speaking, coughing, or sneezing. Second, the power of the light source, the properties of the fluorophore, and the dynamic range of the human eye probably limit the analytical sensitivity of the test. Finally, it is widely thought that the respiratory droplets most likely to spread infection through aerosols have diameters ≤5 μm (Fennelly, 2020) and median droplet diameter for propellant-driven hairsprays like ours is approximately 25 μm (Kim et al., 2019). Thus, a mask could theoretically prevent almost the entire fluorescent signal in this test method but still allow infectious virus particles to pass through. So it must be stressed that this is not a test of the ability of a mask to prevent virus infection or transmission. Nevertheless, around 5–10% of hairspray droplets are in the 1–10 μm range (Sciarra et al., 1969; Kim et al., 2019) so the test could have some value to detect even those small droplets. Furthermore, the utility of the 5 μm diameter cutoff is somewhat controversial in the first place. For example, a droplet that starts at 10–100 μm quickly becomes a 1–5 μm particle (or even simply the remnant nucleus) within milliseconds to seconds through evaporation of these very small liquid volumes (Morawska, 2006). Since liquid droplets in this range can remain in the air for seconds to minutes, that is more than enough time for some of them to evaporate and become cause for concern (Morawska, 2006). Moreover, larger droplets deposited on surfaces that we touch or in the upper airways may still be trapped or absorbed and lead to infection. Finally, the widely used 5 μm cutoff seems to be based in part on toxicology studies of particulate matter (PM) inhalation (for example, Brown et al., 1950; Morawska et al., 1999), but solid PM is obviously not subject to evaporation in the air or absorption in tissue in the same way as respiratory droplets and their content. Therefore, it is likely that the method presented here provides at least some indication of how well a mask works to reduce aerosol and droplet spread, though it should not be considered a test of infectiousness. It is also inexpensive, fast, and can be assembled using widely available resources. Overall, we conclude that this is a rapid and convenient test that the average consumer may use to compare the barrier function of their masks to determine which mask in their wardrobe likely offers the greatest protection.

FUNDING

This project was funded in part by funds from the Translational Research Institute at the University of Arkansas for Medical Sciences that is supported in part by National Institutes of Health grant UL1TR003107 and from the Arkansas Biosciences Institute, which is the major research component of the Arkansas Tobacco Settlement Proceeds Act of 2000.

REFERENCES