I bought one of these window masks. The transparent plastic window blocks air. So it's safer to people in front, though I can't be sure about other angles. Also it fogs glasses more.
The first time I went out wearing it, a guy in the elevator asked me how breathable it was. I told him that it was about as good as fabric, and the air mostly flows from the back and sides.
Just after leaving the elevator, I noticed that my pants zipper was down. Fortunately, I don't think the guy noticed. I'd be embarrassed if he thought I was really into windows.