How Safe and Effective is Re-Using a KF94/KN95 Face Mask?

Main Takeaways

• It’s reasonably safe. Contracting Covid-19 from surfaces (e.g., masks) isn’t likely. The virus may not survive that long in real life due to light, heat, etc. Rotating the use of 3 masks (one per day) can be a good compromise between safety and re-use. Regardless, please also continue hand washing.

• The filtration efficiency only lowers 2-3% from extended use (~40 hours) of the same KF/KN mask in an average environment.

Safety

Early studies of the virus' lifespan on surfaces were conducted in a tightly controlled laboratory, not a real-world setting. Based on recent evidence, there may be no reason to disinfect surfaces obsessively. The virus may not survive that long in everyday life. Temperature, light, humidity, and ventilation all affect virus viability and concentration. Regardless, regular hand washing is still always needed.

Also, the severity of Covid-19 may depend on the amount of viral load you’re initially exposed to [10][11][12][13].

Less virus = fewer complications.

Note: Most KF/KN masks are not designed for cleaning, so it’s probably not a good idea. It can affect mask integrity.

Effectiveness

Over the past half-year, Aaron Collins, a mechanical engineer who wrote his masters’ thesis on aerosols, has selflessly spent hours testing numerous masks (mainly KF94 and KN95s). In full transparency, he compiled all his data and observations in a Google Doc. The videos he posted on YouTube also highlight the sizes and features of different masks. He’s also been very active on Reddit.

Most KF94/KN95 masks he tested were well above 90% efficient. After around 40 hours of use, he only noticed a 2-3% filtration reduction with BOTN KF94 masks.

Another BOTN mask was used randomly, kept in the car for over 3 months, and accidentally left in the rain. After drying, it was still 90% effective.

Cloth Masks

The two cloth masks he tested had 53% and 55% filtration efficiency.

Surgical Masks

Filtration efficiency of different loosely worn surgical masks vary widely: 11%, 27%, 41%, 76%, 84%

Conclusion

Even a heavily used KF94 or KN95 is still vastly more effective than any simple cloth or surgical mask.

Collins’ personal opinion on mask re-use based on his tests and observations:

• 30–40 hours in a clean office-type environment.

• Fewer hours if you're in a construction-type environment or if you're exposed to a lot of aerosol.

• If you're in a super-clean environment, potentially even more than 30–40 hours.