German scientists did a test to find out the best way to stop the flow of air from a cough. They used a method that allowed them to SEE the air as it dispersed from a man's mouth. First they had him breathe normally, and then do an open-air cough.
Then he coughed into his hand, into his sleeve, into a dust mask, and finally into a surgical mask. None of the methods completely stopped the flow of air, but the one that worked best was when he coughed into his sleeve or elbow.