According to the director of the Center for Disease Control Robert Redfield, "It’s not a decision to try to protect me from getting coronavirus, It’s to help modify spreading. And there is scientific data to show that when you aerosolized virus through a cloth barrier, you have a reduction in the amount of virus that gets through the other side."
Critically, the CDC emphasizes that cloth face masks should be used by the general public to conserve surgical masks or N-95 respirators for medical workers. These medical-grade masks are in woefully short supply.