AUSTIN (KXAN) — Researchers at Duke University have developed a new tool to find the effectiveness of the various types of masks people are using to stop spread during the COVID-19 pandemic.

And some offer less protection than others, researchers found.

STUDY: Low-cost measurement of facemask efficacy for filtering expelled droplets during speech

So which masks are the best — and the worst?

Duke researchers say, naturally, the most effective mask was the N95. The Centers for Disease Control and Prevention explains that N95 are not only masks, but respirators that filter out at least 95% of particles in the air. N95s also fit more securely than a regular face mask does, allowing for minimal leakage.

Other masks that performed well in the test were three-layer surgical masks and cotton masks — which can be made at home.

Worst performers, researchers say, were folded bandannas and knitted masks.

Shockingly, in some cases, certain types of masks made particle exposure even worse, according to the study.

The authors of the study say that neck fleeces, also known as gaiter masks, were the least effective of all.

“We were extremely surprised to find that the number of particles measured with the fleece actually exceeded the number of particles measured without wearing any mask,” Martin Fischer, one of the study’s authors told CNN. “We want to emphasize that we really encourage people to wear masks, but we want them to wear masks that actually work.”

Neck fleeces were shown to break down larger droplets into smaller particles, which can more easily slip through and out.

Below are the range of masks that the Duke study tested.

(Duke University)

The test

The experimental setup is relatively simple: someone wearing a face mask would speak in the direction of a laser beam inside a dark box. Then, the amount of droplets that scattered in the laser’s beam were recorded with cell phone camera — this is pictured below.

That data was then counted using an algorithm.

See more charts and findings of the Duke University mask experiment.