I've used it to make windows on steam locomotives, typically the cab front and rear windows. It can be challenging as it dries thick at the window frames and thin in the window centers due to surface tension when applying it. Sometimes multiple applications are necessary. You can't go too thick, because it can skin over and the stuff under the dry skin won't turn clear because it can't fully dry. I don't use it on large windows or on flat areas where more conventional materials serve better.