@Warm Soda, I appreciate your willingness to share what you learned. While you have more experience than I, I have an idea why you had so much trouble with the material. I noticed that you were harvesting in March. Reading that article on Mother Earth News suggests that the ideal time would be late fall. You posted a picture of what the cat tails looked like where you were gathering them. Again, I haven't harvested any myself yet (why couldn't I have seen this 2 months ago!?!?), but I'm wondering if the specimens you collected were not ideal. I would think the "fluffiest" cat tails would have "popped" in the fall, so any that were still around near Spring would not be ideal. Some of the cat tails in your picture appeared to be shedding some fibers, it seems to me that these are all the ones that couldn't grow the seed tails enough to actually disperse them, no? One of the links posted on this thread showed someone "popping" cat tails in the wild. Did the ones you harvested do that too? I suspect the ideal cat tails will be the ones that are almost ready to pop on their own. This would indicate the seed tails were fully mature and would provide maximum loft.
Again, this is in no way trying to disparage your effort. Your quilt is awesome! I'm only posting my thoughts in hopes it will help us find a way to use this natural material in a way that would produce a lighter quilt.
Thanks again to Xexorz and everyone, especially Warm Soda, for collaborating on this research. I thought about going and looking for some cat tails myself, but I'm afraid I might end up in the same situation by not harvesting at the peak time.