They are styrofoam balls with flowers attached hung by a ribbon. Rather than using real flowers (cha-ching...can't you hear the sounds of a cash register?) we used tissue paper. Both of us were really skeptical if it would look tacky or cheap, but it turned out great. The process of making them is definitely a labor of love, but I have plenty of time to prepare. I'm a planner. I don't like to be rushed and I am glad I can take my time with these.
Here are a few pics (the pom pom is not totally complete yet. I still need to add a ribbon to hang it, but you should get the idea).
Here is one of the tissue paper flowers
most of the pom pom..
it has about 30 flowers in it right now