Starching a hat is a great way to shape it the way you want it. You can starch a baseball cap to get the perfect curve on its brim, or a floppy hat that would otherwise be hard to wear. While you can purchase starch, it may be easier and cheaper to make it at home.
Make the starch water. Boil 3 ¾ cups of water in a pot. While the water is boiling, make a starch paste by adding one tablespoon of corn starch to one tablespoon of cold water, mixing the two until they resemble a paste. Add the paste to the boiling water. Stir the mixture continuously until the starch paste dissolves. Simmer on low heat until the liquid thickens. Allow the liquid to cool, then pour it into the spray bottle.
Shape the hat. Before you starch your hat, decide how you want it to look after it stiffens. Shape it carefully into that shape before spraying the starch. Use a rubber band to curve the brim of a baseball cap.
Lightly spray the hat after it has been shaped and allow it to rest overnight. The next day the hat should keep its shape.