The "double mask" thing is based on 1 preprint experiment. Buried in the conclusions: "The findings of these simulations... should not be interpreted as being representative of the effectiveness of these masks when worn in real-world settings." User squaremild, in the conspiracy subreddit, 16 Feb 2021
Making masks fit better can reduce coronavirus exposure by 96 percent. Even if only one person is wearing a mask tweaked to fit snugly, the wearer is protected from 64.5 percent to 83 percent of potentially virus-carrying particles User Willybud, in the coronavirus china subreddit, 14 Feb 2021
Making masks fit better can reduce coronavirus exposure by 96 percent. Even if only one person is wearing a mask tweaked to fit snugly, the wearer is protected from 64.5 percent to 83 percent of potentially virus-carrying particles User worldnewsbot, in the News From Around The World subreddit, 14 Feb 2021
Maximizing Fit for Cloth and Medical Procedure Masks ... User D-R-AZ, in the Novel Coronavirus (COVID-19) subreddit, 13 Feb 2021