Helmet, not Mask
Health professionals wear a face shield and a mask. But it strikes me that a combination (a clear covering over the entire face, but sealed with a filter like a mask) would serve them and us a lot better. The idea of a face-covering plus filter could fit onto bicycle helmets, football helmets, cowboy hats, and all sorts of other items we might wear. It could have a window that opens and reseals for eating and drinking. It could come in versions that gave a clear view of the face or did not, depending on the purposes to be served. A quick version would simply velcro "filter-quality cloth" to the outside edges of an existing face shield, but I suspect Xprize teams could do way better than that.