How to make my comforter more fluffy?

SO, about 2 years ago I got new comforters. (I have two twin sized beds. I dont share the room with anybody, I just ended up with 2 beds lol) They are the fake down (I'm allergic to the real stuff so....) and were really fluffy when I got them. Now they are kinda flat and boring. I ung tem up on the clothesline on a windy day and they are still really flat. I dont really want to put them through the drier because the last ones I had got really clumped and lumpy. :(