Masks work. Really. We'll Show You How. The New York Times

https://www.nytimes.com/interactive/2020/10/30/science/wear-mask-covid-particles-ul.html/

By Or Fleisher, Gabriel Gianordoli, Yuliya Parshina-Kottas, Karthik Patanjali, Miles Peyton and Bedel Saget  

The public health debate on wearing masks is settled, said Joseph G. Allen, director of the Healthy Buildings program at Harvard. "When you wear a mask, you prevent yourself from touching your face," he said. And you signal that wearing a mask is the right thing to do.

With coronavirus cases still rising, wearing a mask is more important than ever. In this animation, you will see just how effective a swath of cloth can be at fighting the pandemic.

Masks come in many styles and materials, but they generally work in the same way. Layers of fibers capture large respiratory droplets and smaller airborne particles known as aerosols that can carry the coronavirus.

This process is known as filtration, and a material's ability to trap particles is called filtration efficiency.

Tightly woven cotton outperforms most common fabrics. A nonwoven like that of an N95 respirator is most effective.

Let's take a closer look at how filtration works at the microscopic level.

Here is how the fibers of a cotton mask compare with the aerosol particles of different sizes. The coronavirus is about the same size of the smallest particles, but it usually travels inside the larger ones.

The fibers present a dense forest that the particles must navigate as they move with the air stream. The laws of physics influence how the particles interact with the fibers and how well the mask can capture them.

Larger particles are easier to trap. They slam straight into the fibers and get stuck when the air stream brings them within touching distance, or when their momentum causes them to veer off course.

The smallest particles are bounced around by air molecules in a random zig-zag motion, increasing the time they spend in the fiber forest and their chances of getting captured.

Medium-sized particles are the hardest to filter. They evade capture because they follow the air flow, twisting and turning around the fibers.

Here are the fibers of an N95 respirator. They are made of synthetic fibers, vary in size and are arranged randomly. And they have an extra feature: an electrostatic charge that attracts and captures particles of all sizes.

Where most masks fall short, N95s excel. Their material can filter at least 95 percent of the elusive medium-sized particles and even more of the small and large ones.

Fibers are not the only factor in filtration. Masks of all kinds vary in filtration efficiency based on their size and shape.

Loose-fitting masks or those pressed against facial hair allow aerosols to leak.

A good mask will have a large surface area, a tight fit around the edges, and a shape that leaves space around your nostrils and mouth.

This creates a larger breathing zone to catch the particles and increases the chance they will encounter a fiber.

Some masks have valves which make it easier to exhale, but without filters, these valves do not trap the aerosols you breathe out, so they do little to protect others.

A well-fitting N95 is the gold standard, but don't worry if you can't get your hands on one. When everyone wears a mask, the combined filtration efficiency increases.

Let's say the mask you're wearing filters half the particles you exhale. The particles that escape disperse through the air and are further diluted.

The particles that eventually reach someone else's mask get filtered, reducing the number that get through.

"It's become clear that cloth masks, even though not as effective as N95s, are still effective in reducing transmission," said Linsey Marr, an aerosol expert at Virginia Tech. "Even though you're not achieving that 95 percent reduction, something is better than nothing."

Good ventilation and social distancing further reduce the risk of transmission. And if everyone wears their mask and keeps their distance, the collective benefits go up.

Stand inside an N95 respirator to see how it works. The augmented-reality experience lets you stand inside the magnified fibers of an N95 respirator to see how it filters aerosols. Launch aerosols of different sizes and see how they are captured by the fibers of the respirator. To experience this in your space, you will need the Instagram app.

To view on Instagram, open the camera on your device and point to the QR tag below.

NOTE: You will see this prompt at the end of this article.