The best and worst choices for a cloth face mask

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A bandana is the least effective face mask you can wear to protect others, according to a recent study.

There are few studies on face mask fabrics, but the current consensus is that tight-weave cotton is the best material for a cloth mask.

This mask has two layers of cotton.

Pleated face masks allow more air circulation inside the mask, making it less likely air will escape through the sides.

A cone-shaped mask is more effective than a flat-front design in stopping incoming and outgoing droplets.

Any face mask is better than no face mask during the pandemic. But all masks are not created equal.

Anti-maskers argue that forcing someone to wear a face covering is an infringement on rights, such as the right to decide what represents an acceptable risk to oneself. That's the same argument that bareheaded motorcycle riders made before helmet rules went into effect.

When it comes to masks, however, the infringement justification does not hold water. The primary duty of a face covering is not to protect the wearer like a helmet does, but to protect others. If you are COVID-19 asymptomatic and you refuse to wear a mask in public, your body effectively becomes a bioweapon.

The Centers for Disease Control and Prevention says the general public should wear cloth face coverings, not medical-grade N95 masks and surgical masks. Those should be reserved for health-care workers and first responders.

So what are the best — and worst — cloth masks for everyday use?

—Bandanas are the least-effective. In a Florida Atlantic University study, scientists found that droplets from a bandana-covered cough traveled 3 feet, 7 inches, compared to 8 to 12 feet with no mask at all. Holding a double-folded handkerchief over one's mouth was much more efficient — it stopped droplets from going more than 1.25 feet.

—Get one made of cotton. Tightly woven, 100-percent cotton works well. Christopher Zangmeister, a researcher at the National Institute of Standards and Technology and co-author of a new study published in ACS Nano, told NPR that microscopic cotton fibers have a more three-dimensional structure than synthetic materials, which makes them more efficient at snagging incoming particles.

—The more layers, the better. Two layers of tight-weave cotton are good, three or more are better. The CDC recommends at least three fabric layers, which can include a middle layer of filtering material.

—Masks with a filter pocket between two layers provide more protection. A two-layer, tight-weave cotton mask alone can filter out about 35% of small particles, Stanford University Professor of Materials Science and Engineering Yi Cui told NPR. But if a filter made out of two layers of charged polypropylene is placed in the pocket, the mask's filtration efficiency could double to up to 70%. Polypropylene, also known by the brand name Oly-fun (Walmart) and spunbond, holds an electrostatic charge that traps incoming and outgoing particles.

In March the Czech Republic knew and implemented a mask policy. It appears that a lot of resistance was because of a ‘not invented here’ attitude. https://t.co/iY13P74ONB

—Fit matters. It's important that a cloth mask seals snuggly to your face. If gaps open up where the mask touches the skin, its effectiveness is compromised. Folded, pleated and duckbill masks allow more air flowing through the fabric and less leaking out the sides compared to a flat-front mask.

—Neck gaiters, tubes or buffs, which cover the nose down to the neck, solve the air-leakage problem. Many people find them more comfortable than masks because they don't have ear loops or ties. However, they are generally made of polyester and/or spandex, which are less effective at filtering particles than cotton. Some come with filters. Sample complaints from product reviews include: too hot during the summer, easy to slip off nose, filter does not stay over the mouth.

—Don't buy a mask with a vent or exhalation valve. While they make breathing easier, vents defeat the mask's purpose because they release unfiltered air that can contain droplets. Industrial-grade N95 masks designed for smoky or smoggy environments often have these valves.

Reports of stores and other businesses barring entry to customers wearing vented masks are increasing. If you already own one, either put a second mask over top of it or completely cover the vent with tape or a sewn-on patch.

Exception: Some vented masks have filters that trap exhaled droplets, making them safe for others. However, it's not possible to tell whether a valve is filtered or not just by looking at it. Mayo Clinic guidelines prohibit the wearing of masks with valves or vents.

—Make sure your mask is washable. Unlike medical masks, which are normally designed for single-use, cloth masks should be washed after every use and worn until the fabric or structure breaks down.

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Mike Moffitt is an SFGATE Reporter. Email: [email protected]. Twitter: @Mike_at_SFGate