Last updated 2021-04-02
Specifications for masks for sale
People making masks for sale should specify the materials (composition, weave, weight, thread count) for each layer and the number of layers (e.g., cotton 100%, plain weave, 150 gsm, 300 TPI; spunbond polypropylene 70 gsm; outer layers cotton, middle layer polypropylene). Useful information for mask manufacturers can be found here.
Choosing to wear a mask
Studies showing that community transmission decreases when mask mandates are put in place show that the cloth masks that are in general use have the ability to impact this pandemic. We think that most cloth masks in current use reduce contamination of the environment and reduce particles reaching the wearer. This website aims to help people choose and make better masks, to get the most protection that they can, and to best protect others.
Level of exposure
How many people? The more, the higher the risk.
Will the other people be wearing masks?
How close will other people be, and is there a risk that physical distance might be unexpectedly compromised?
What is the duration of the activity? The longer, the higher the risk.
Will people be talking loudly, shouting, singing or eating? These activities create many more aerosol particles than quiet talking.
Is the activity indoors or outdoors? Outdoor activities are lower risk, but not no risk.
Level of activity
People who are exercising may prefer a more breathable mask; however, exercising indoors with others is a high-risk activity so attention should also be paid to materials and fit. People exercising outside who will be passing others should wear a mask.
Level of personal risk
People who are older or from a vulnerable group, and people who are risk-averse for any reason (e.g., living with or caring for someone from a vulnerable group), may be prepared to wear more layers, even though it may be less comfortable.
Bandanas and scarfs
These same materials would be recommended if using a bandana or scarf-type design, though we would anticipate that this would be less efficient. Optimally, this will include a prefolded shape, and a clear differentiation of outside and inside, such as this video showing a multi-layered suggestion.
We do not recommend household materials such as furnace filters or dried baby wipes. Evidence on household filters is limited. We found one study of tissue paper and paper towel, which did not report high efficiencies. Instead, we recommend a third or fourth layer of industry grade polypropylene. If you have pocket masks, you can use a rectangle of this material as a reusable filter in a pocket mask and wash it with the mask - just remember to hang to dry - it will melt in a tumble drier.
There is evidence that securing the mask over the head instead of on earloops improves the effective filtration, probably by improving fit and reducing edge leak. To simplify the design and construction, our beginner's mask has buttons sewn on the corners and ordinary rubber bands, looped together, to provide over-the-head elastic. We borrowed this idea from N95s, which offer a high level of protection to health-care workers; these usually have over-the-head elastic straps. Elastic perishes with multiple washes, and the button design facilitates easy replacement. Sewn elastic, ear loops and cloth ties are alternatives.
Don’t touch your face when wearing your mask. Learn how to take off a mask safely here, and wash your hands afterwards.
Children under 2 years, people having breathing difficulties, and people who cannot remove their own masks should not wear masks. Check that masks for children don't have pieces such as toggles and buttons that can become separated and pose a choking hazard.
Though we are sure that many kinds of cloth block particle transmission, including aerosols, and including viruses, we don’t have direct evidence from clinical trials that wearing a mask reduces actual disease transmission in a community setting. We suggest wearing a mask altruistically, with confidence that this is reducing the contamination of the environment. We suggest remembering people who rely on lip reading to understand what is said. We suggest withholding judgement on those not wearing masks, given that their personal circumstances and physical health are unknown.