You'll see on many of my design tutorials that you are instructed to wrap the foam with waterproof tape. Do you know the reason why?
As you are probably already aware, florist foam is soft and easily broken apart. More weight is added when you float soak that floam. Many of the designs show numerous flower insertions in a small amount of foam.
Wrapping the foam (after the soak) is an extra precaution that keeps the integrity of the foam intact. Oasis has added Netting to their spheres, but it is still wise to wrap those balls with a grid of waterproof tape.
If your design is filled with a lot of flower stems in a single piece of foam, I also recommend that you use Floralock Stem Adhesive in order to have the flowers securely glued in place.