Various types of umbrellas will make it a bit cooler by creating shade but it will still be HOT in the summer @ Disney. The problem is their size and how to manage them in crowded places like Disney. Some people are too self-absorbed to notice those around them and thinking by having an umbrella the waters will magically part to keep others away from you seems a bit unrealistic. For the majority of people, they aren't going to make that much of a difference and would be annoying to have it open when it isn't raining.