Can Face Masks with Carbon Filters Provide Better Protection Against the Coronavirus?

Throughout the winter, spring, and summer of a global pandemic, many individuals have become accustomed to wearing a cloth face covering to minimize the transmission of the coronavirus, a highly contagious virus that seeks out human hosts. Masks serve to block the emission and inhalation of respiratory droplets, which can carry the virus.

Recently, numerous cloth face masks—both homemade and mass-produced—available for purchase online have advertised the inclusion of a carbon or other filter designed to enhance the mask’s effectiveness, potentially blocking even more viral particles than the mask alone. Does this extra filtration really provide any additional benefit?

Health experts confirm that, yes, additional filters can help—but it's important to be cautious about the type of filter selected.

Filters are usually placed between two layers of cotton, or alternatively, some mask providers offer masks with a pocket for a filter of your choice. Certain filters are advertised as HEPA-certified, a standard for air filtration, or as carbon-based, potentially enhancing the material’s ability to trap particulates, preventing them from passing through the mask. While these filters are commonly used in air purifiers, their effectiveness when used in face masks remains unverified.

“Carbon and charcoal are designed to filter contaminants from water,” says May Chu, Ph.D., a clinical professor of epidemiology at the Colorado School of Public Health Anschutz Medical Center, speaking to Mytour. “We don’t know if inhaling charcoal particles or fragments is healthy for your lungs.”

The same concern applies to using vacuum cleaner bags or coffee filters. Some, Chu notes, are made from silica fibers or glass, which are not substances you want in your lungs. “These are not meant for breathing,” Chu emphasizes.

According to Chu, the key feature of an effective mask is its ability to balance particle filtration with comfort and breathability. While a very thick mask might prevent droplets from passing through, it could also make it difficult to breathe and may lead to inhaling through the mask's sides, where no barrier exists.

Cotton is the preferred material for masks. A tightly woven cotton fabric allows airflow while capturing particles more effectively than smoother synthetic materials. Cotton tends to perform best with multiple layers, especially if light can’t easily pass through it. If light does shine through, the fabric is likely too thin.

Since cotton alone isn’t specifically designed to block particles, adding a filter can improve its protective qualities. However, like the mask itself, the filter should be made of a safe material that is comfortable to wear. Chu suggests polypropylene, a material available under the brand Oly-Fun at Walmart and other stores, also marketed as Spunbond.

What makes polypropylene stand out? “It’s the same material used in N95 masks,” Chu explains. N95 masks, worn by healthcare workers, filter up to 95 percent of airborne particles. However, Chu cautions that consumers should recognize that the polypropylene used in stores differs from the kind used in medical-grade N95 masks.

“N95 polypropylene is specially calibrated and designed for a specific level of filtration with a set standard,” Chu clarifies. “It’s more expensive and precisely manufactured.” Two layers of Spunbond polypropylene can come close to—but not replicate—the protective capabilities of a single layer of medical-grade mask filters.

Polypropylene works effectively because it can retain a static charge that repels particles. While an N95 mask is designed to maintain this charge throughout its use, you can generate a charge in a homemade filter by ironing the polypropylene or rubbing it with a plastic glove for 20 seconds. This charge will last about 12 hours or until the filter is washed, according to Chu.

A surgical-style mask can also serve as your filtration layer, as medical-grade masks are typically made with polypropylene.

If polypropylene isn’t available, there’s an easy alternative that almost anyone can use. Simply insert four sheets of Kleenex (or two folded sheets) into the mask’s pocket. “Kleenex provides good efficiency in blocking particles while still allowing for breathability,” says Chu.

Regardless of the filter used, it’s crucial to remember that once a mask or filter gets wet, it loses its ability to hold a charge (in the case of polypropylene) or block particles (for facial tissue). The filter must be dried or replaced to maintain its effectiveness.

While medical professionals naturally opt for N95 masks when available, what does Chu do when wearing a cloth mask? “I wear a locally made mask,” Chu says. “It’s two layers of polypropylene, with cotton pockets in the front and back.”

When combined with social distancing and proper hand hygiene, a breathable mask with a safe filter can help slow the spread of the virus by reducing the number of infectious droplets released from a person’s mouth. “That’s why masks are effective,” Chu explains. “That’s what we know works.”