Like GLP said, the stuff is heavy (compared with down). But it WILL keep you warm. I believe someone also mentioned that you want to bake it in the oven to kill insects that will undoubtedly be in there (seen & unseen). I've collected some cat tail fluff and plan on making an UQ when I collect some more. That plus some cheap silnylon and a little bit of sewing = a nice, cheap car-camping UQ!
At least thats the plan.... Good luck with your project!