Dave , I am fairly sure about that, I delibertly poured some on damp cloth and let it set for a bit then dumped it on to a dry cloth and rolled the cloth up and worked it around to take any excess off; the logic being if the powder absorbed the moisture like some will it would miss fire, all three shots fire with out any hesitation so I believe that it is at least resistant to humidity. I looked carefully at the holes in the paper besause they looked a bit different, I did not expect the rain to affect the flight of the bullet. I think I won't be taking any long shoots in the rain any way, but it would be nice to know just what effects it can cause; look how far just a good strong breeze can move one in a hundred yds. Lee