Yes and it's actually a sensitive test for fit. If you get fog then air is leaking out unfiltered, so when you breathe in, it's also not filtering that part. I

Yes and it's actually a sensitive test for fit. If you get fog then air is leaking out unfiltered, so when you breathe in, it's also not filtering that part. It's imperfect bc you can have gaps around your chin which won't fog up. But it's one of the nice parts of the good filtered masks. And in the winter it helps keep the bite of cold away