Gum paste is a sugar dough from the same family as rolled fondant that is used to create brittle sculptures for decorating cakes. It's made from confectioner's sugar, gelatin, Gum Tragacanth (or Gum Tex), liquid glucose, and water. Unlike fondant, gum paste stretches very thin and dries without cracking, which makes it great for creating dramatic, delicate flower petals. It's brittle when hardened, which also makes it useful for decorators, because there is no worry that flowers will melt or bend once they have set.
'cake decorating' on Serious Eats
Decorating cakes the way the pros do takes years of dedication and practice, but knowing a few cool tricks can definitely make the difference between a boring cake and a cake that looks elegant and special. With just a basic set of metal piping tips, there are many impressive designs that you can create to jazz up a cake.
Now that it's become de rigueur to cover and decorate celebration cakes with fondant, the flexible sugar dough that's become exceedingly popular thanks to cake TV shows, Swiss buttercream has become an afterthought. For me, a cook who believes that it's never worth it to sacrifice flavor for appearance, the demise of buttercream cakes is a travesty.