Scientists recently tested 14 types of masks, and they found that bandannas, and gaiters are the least effective at stopping the spread of coronavirus. N95 masks are the best at containing potentially virus containing droplets.
To test the masks, scientists at Duke University used a black box with a laser and a camera. Someone wearing a face mask would speak in the direction of the beam inside the box. The amount of respiratory droplets scattered by the beam were recorded by the camera in the back of the box.
Three layer surgical masks and cotton masks, which can be made at home, performed well. The researchers were surprised to find that neck gaiters actually spread more droplets than not wearing a mask at all. They were shown to break down larger droplets into smaller particles, which then slipped out the sides of the covering more easily.
The full study can be found here.