I've heard that Camp Dry silicone spray works very well for waterproofing feathers.

Today I went to a 3D shoot.. and it was drizzly rain all day... that is until we were done shooting.. which meraculously the rain stopped just as we were walking out of the woods. I use 3" feathers on my 3D arrows... and they were SOAKED!!!... hadn't waterproofed them because I hadn't planned on shooting them in the rain. Well they got all nice and matted.... and I would have a big puff of water whenever I shot... Needless to say the arrows still flied perfect and I shot the best in our class... I've never seen feathers that matted.. They looked like those arrows that you find that have been "lost" in the woods for who knows how long. I know broadheads are a little different story. But just thought I'd share this experience...