I use something along the milkweed lines, they arethese little, fine feathers I take from my chickens (stomach and pelvic area)when I butcher them. I have bags and bags of them and they work great. I can even shred the feather into smaller pieces that will ride thermals and real see what the wind is doing all around me. I'll send out about 5-7 little floaters at a time and it is very interesting to see where they all go sometimes. I stuff a bunch in a film canister and keep it in my pack.