I made one from thin, open-cell black foam covered with fly-screen mesh. Took a while to sew it together and add a springy nose piece (metal strip inside heat shrink tube). Useful for keeping flies out of mouth. It's see-through but you can't tell that when it's on my face.

Of course I wear it only when there's no alternative. Most of the shops are happy if I simply dangle it around my neck.