Things You'll Need
Rolled fondant is basically an edible version of the modeling clay you used to use in art class. You can roll out fondant flat or use it to make 3-D cake decorations, such as balloons. The finished balloons can be place flat on top of a cake, but to really make the 3-D quality apparent, stand them upright on the cake, using wires that resemble balloon strings. This works well with packaged fondant in an assortment of colors or you can make your own marshmallow fondant and color it with food coloring gel.
Pull off a piece of the rolled fondant icing. You don't need to roll the fondant flat to make balloons, but simply pull a small piece off the larger ball or block of fondant.
Roll the fondant in the palms of your hands to form a smooth ball shape. Dip your fingers in vegetable oil if the fondant feels dry in your hands. The vegetable oil also makes the balloons shiny.
Hold the top half of the ball between two fingers with your non-dominant hand. Pull the bottom half down with the fingers on your other hand to create a slight rounded taper for the bottom side of the balloon.
Pull off another small piece of fondant and roll it out flat with a fondant roller. Cut it into a thin strip. Roll the strip around the end of a toothpick and pinch one end closed around the end of the toothpick. Slide the rolled strip off the end of the toothpick. Press it centered on the bottom of the balloon to create the small flap on the opposite side of a balloon knot.
Cut a piece of thin wire such as floral wire with a pair of wire cutters. Push one end of the wire into the bottom of the balloon, inserted through the open end of the rolled fondant piece. Cut one wire for each balloon and repeat this process. The length of the wire depends on how high you want to set the balloons, but don't make it too long or the wire could bend over with the weight of the fondant.
The amount of fondant needed depends on the desired size for the balloons. The strip for the balloon knot must be to scale with the balloon size. Fondant balloons aren't practical for mounting on wires if they're more than about 1 1/2 to 2 inches long because the fondant is just too heavy. You can try a heavier gauge wire, but thicker wire is more noticeable on the cake.