On the surface, this may seem crazy, performing a drop test on a glass ND filter, but, hear me out. I've been speaking with Breakthrough Photography about their filters and one of the things that came up was the fact that their filters are made of tempered glass. They seemed really confident about how strong their filters were so I, of course, wanted to know how strong. After a few initial, probing questions, I asked them if I could do a drop test on their filters to demonstrate their durability. To my surprise, they not only agreed but, they sent me an extra filter specifically for the test.