A large, randomized study done in Bangladesh offers strong evidence; surgical masks were also more effective than cloth masks. An informative news account here; an excerpt:
Among the roughly 178,000 individuals who were encouraged to wear them, the scientists found that mask-wearing increased by almost 30 percent and that the change in behavior persisted for 10 weeks or more. After the program was instituted, the researchers reported an 11.9 percent decrease in symptomatic Covid symptoms and a 9.3 percent reduction in symptomatic seroprevalence, which indicates that the virus was detected in blood tests....
"A 30-percent increase in mask-wearing led to a 10 percent drop in Covid, so imagine if there was a 100-percent increase — if everybody wore a mask and we saw a 100-percent change," he said.
