With 21 U.S. states experiencing a rise in Covid-19 cases just weeks after reopening, it’s clear that maintaining control of the pandemic without lockdowns is proving to be a challenge. To not only stay open but also really revive the economy — to get people back to work, traveling, attending sporting events, eating at restaurants, and so on — they will need to feel confident that they and their loved ones are at low risk of getting infected.

Testing remains an order of magnitude short of what is needed, and a vaccine won’t be available until at least early next year. But we could potentially achieve control and confidence now if better masks were available for the general public that are more protective than the cloth ones worn now and closer in caliber to the N95 and high-filtration surgical masks used by health workers. In a previous article, we underscored the need for such masks in order to reopen safely. Now, as cases surge, we explain why better masks are as important as ever and outline the criteria for their effective design.

Scientists believe that Covid-19 is largely transmitted via virus-containing particles that people emit when they breathe, speak, cough, or sneeze. N95 masks, if worn correctly, can block nearly all of this spread. High-filtration surgical masks, which are a cut below N95s, can block much of this transmission but are not as effective against smaller particles, known as aerosols.While we need to better understand the level of protection required, what is clear is that if we had better masks than current cloth and homemade ones, transmission could be substantially and quickly curbed.

Consequently, we need masks for the general population that block the virus from coming in and going out similar to what high-filtration surgical or N95 masks do for health workers. Masks like this would give people control over their own safety, a greater incentive to wear them, and the confidence to resume economically important activities.

If worn widely enough in crowded and indoor settings where most transmission seems to occur, these masks could potentially stop the epidemic altogether. They would also reduce flu transmission and the chance of a dreaded “double epidemic”in the fall. Better masks may be the most effective way to counter Covid-19 in low-income countries where testing is limited and the social and economic damage caused by lockdowns is more severe.

These masks should meet five parameters:

Protection

The level of necessary protection depends on how important it is to defend against aerosols. Protection results from deflection and filtration (how well particles are blocked going through the mask) and fit (how well the mask seals around the face and prevents particles from coming around it).

Scalability

Any design must use commonly available materials that commercial manufacturers can purchase in massive quantities. Multiple designs using different materials may be necessary so we are not reliant on any single set of materials that could run out. One reasons masks are such an attractive option is that, unlike testing and contact tracing, they can be scaled more readily and widely.

Comfort

Masks must be comfortable enough for people to wear them for long periods of time without needing to touch them or take them off too frequently. There may be ways to do this while still preserving protection.

Reusability

To preclude a constant need for new masks, it would have to be possible to easily clean them or only have to replace certain parts (e.g., filters) so they could be repeatedly used.

Style

Widespread adoption of masks will require a significant cultural shift so they become a seamless part of a “new normal.” They should be fun, cool, and fashionable. For instance, they might exhibit the colors or logos of individuals’ favorite sports teams or brands.

Designing and producing such masks and persuading large numbers of people to wear them is not straightforward and poses engineering, manufacturing, and marketing challenges that may ultimately require tradeoffs. Academic institutions, companies, and private citizens can start creating and testing designs and mass manufacturing effective ones. Industries imperiled by the epidemic — such as airlines, sports leagues, and hotels — have every incentive to see this happen and should use their resources and know-how to push this forward.

Once an effective design is in hand, the challenge will be getting enough people to actually wear them in crucial situations. It is difficult for people to wear masks — no matter how comfortable — for hours on end. However, not all situations carry equal transmission risk and wearing masks when performing some activities, such as walking alone outdoors, is less important. It is most critical that masks are worn when indoors, in crowded or tight spaces (e.g., public transportation, bars), in prolonged close contact with others (e.g., sitting across the table at dinner), or engaged in activities that involve heavy breathing (e.g., exercise, singing). Concerted promotional campaigns waged by governments and companies could persuade large numbers of people to wear masks in such places.

Although expanding testing or contact tracing remain crucial, designing, producing, and getting people to wear more protective masks is more feasible and more quickly achievable. It may be the single most important low-hanging opportunity for slowing Covid-19’s spread and giving people the security they need to bring our societies back to life.