Do you have a source for "It's a fact that wearing masks is slowing down the spread by as much as 80%."? There's studies that measure the amount of droplets/aer

Do you have a source for "It's a fact that wearing masks is slowing down the spread by as much as 80%."? There's studies that measure the amount of droplets/aerosol that gets through but I haven't seen any studies about how it affects infection rates.