A new study shows that some face masks may not work as good as we’d hoped against COVID 19.

A group of researchers at Duke University have come up with a way to analyze the effectiveness of different types of face masks.

The person wearing a mask speaks into a hole in a black box.

A laser is used to scatter the respiratory droplets when they talk and a cellphone camera is placed on the back of the box to record the light.

A computer algorithm counts the droplets seen in the video.

The best mask was the N95, followed by surgical and cotton masks. Neck fleeces, folded bandanas and knitted masks performed the worst.