Foam costumes offer endless creative possibilities because they do not have to conform to the shape of your body. The three-dimensional nature of foam makes it the perfect material to make a costume for a fantastical creature, plant or inanimate object. The limits of making foam costumes are only your skill level and imagination. Start with a basic flat shape such as a body-sized star and progress to complicated designs such as dinosaurs, jack-o-lanterns and monsters.
Design your costume. Sketch an original idea or base your design on an image of a foam costume that inspires you. Make a simple foam costume such as a giant star if you have never previously worked with foam. Challenge yourself with more complex ideas such as a monster mask with a movable jaw if you have the experience to do so.
Measure your body to determine how big your costume should be. Make a simple costume such as a giant star (or a banana, or a pizza or any other flat image) large enough to cover your midriff and create a strong visual impact without interfering with your range of motion. Measure the elements for more complex foam costumes based on the proportions in your sketch. Make a foam skirt assembled of tongues of fire with a protruding devil's tail by measuring your waist and leg then scaling the measurements for the tongues of fire and the tail in proportion to your drawing.
Cut the foam pieces to size using sharp scissors.
Attach the foam pieces together to assemble your costume. Leave ample room for your head and limbs. Test the costume's fit by joining the pieces together using duct tape. Ensure that you will be able to get in and out of the costume easily. Duct tape the costume permanently when you are satisfied with the fit. Hot glue the seams of thick foam from the opposite (untaped) side using a cool setting to avoid burns. Press the hot glued pieces together to form a bond. Add additional duct tape to secure the seam. Attach thin foam at the seams using white craft glue.
Create a base for painting your costume by covering it with fabric. Cover the foam costume with white glue. Place the fabric over the foam and glue and smooth it out. Allow the glue to dry until it is no longer wet to the touch.
Trim any overhanging fabric.
Cover the costume with another layer of glue. Allow this to dry completely.
Paint your costume with acrylic paint. Decorate flat costumes such as a giant pizza with a background of paint onto which you may later add 3-dimensional decorations such as toppings cut from felt or from additional foam. Paint elaborate costumes as extensively as you desire, making sure to allow the paint to dry between layers of weathering, gilding or other detailing. Let the paint dry completely before adding three-dimensional details.
Attach details to your foam costume by sewing or gluing. Make monster masks with movable jaws intimidating by attaching an abundance of sharp plastic teeth from a costume store. Refer to images of knights, elves or other magical creatures for more ideas about how to make them feel realistic.