How to wear a surgical mask to capture viruses? Should the blue side be in or out?

Since COVID-19 started, there has been confusion on how to correctly wear a disposable surgical mask. But does wearing face masks the wrong way round affect their ability to capture viruses?

Some online sources claim it doesn’t matter, like this one.

The wrong way wearing surgical masks

Surgical masks are made up of 3 layers, and there is a specific way to wear them: with the colored, rough-textured side out.

wearing masks right and wrong way

But does the direction you wear it actually affect its ability to capture viruses? Smart Air tested sub-micron particle capture to see whether the orientation of a surgical mask really affects performance.

WATCH: What is the Right Way Round to Wear a Surgical Face Mask

How To Wear Your Surgical Mask Correctly - Effects on Performance

Subscribe to Smart Air on YouTube Smart Air Youtube

Testing Surgical Mask Efficiency from Both Sides


To test the surgical masks, we used the same wind tunnel setup that was used for our homemade mask materials tests. In that setup, a fan on one side of a wind tunnel pushes air through the mask on the other end. There, a Met One GT-521 laser particle counter measures how many particles penetrate the mask.

We tested the blue side and white side of four surgical masks.

filteration efficiency tests setup surgical mask

We measured what percentage of particles 0.3 microns and above they could capture. Although COVID-19 is 0.12 microns on average, scientists sampled air in hospitals and found that SARS-CoV-2 sometimes travels on aerosols from 0.25-0.50 microns.

surgical mask particle size

Read More: Are Wet Masks Less Effective?

Surgical Mask Blue vs. White Side Results

Across four masks tested, putting the mask in the correct direction improved particle capture by 1.7% on average. On one mask model, the improvement was nearly 3%.

Four masks filtering efficiency for both 2 sides

Although these numbers are pretty small, wearing face mask the right way will increase its effectiveness at capturing virus-sized particles.

Surgical mask correct way side blue effectiveness

Read More: Do DIY Cloth Masks Protect Us From COVID-19?

Remember: Rough Blue Side Out, Soft White Side In

This data backs up the claim that the colored side of surgical masks (typically blue or green) should face out.  The softer white layer should face in.

Bottom Line: Surgical Mask Direction Affects Performance

Wearing surgical masks with the wrong side out decreases filtration of 0.3-micron particles by 1.7% on average.  Remember to wear your surgical mask the right way–show the world your colors!

Smart Air


Along with wearing masks, air purifiers with HEPA filters are also one of the best ways to stay safe from a variety of pollutants in our air including viruses and dangerous PM2.5. A recent CDC study confirmed significantly lower COVID-19 infection rates in schools that used HEPA air purifiers. HEPA filters can significantly lower the risk of a variety of deadly diseases including diabetes, heart disease, cancer, and high blood pressure.

Read More: Four Steps to Choosing the Best Air Purifier

Smart Air is a certified B Corp committed to combating the myths big companies use to inflate the price of clean air.

Experience breathing truly clean air with gimmick-free, effective air purifiers that won’t break the bank. Join the clean air movement.

Sqair Air Purifier

Free Guide to Breathing Safe

Want to learn more about breathing clean air? Join thousands more and stay up to date on protecting your health.

Notify of
Inline Feedbacks
View all comments
Smart Air low cost purifiers

Smart Air is a social enterprise and certified B-Corp that offers simple, no-nonsense air purifiers and provides free education to protect people from the harms of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.

Certified B-Corp air purifier company