This is my first instructable =) Thanks to my friend who taught me how to do this.
Step 1: Stuff You Need
A hat you don't want anymore (sorry fans!)
A roll of duct tape
Step 2: Wrap the Brim in Duct Tape
You can use scissors to trim off the edges too.
Step 3: Wrap the Front and the Sides of the Hat in Duct Tape
Second, Wrap both sides to the adjustable snap (plastic thing on back) You don't want to cover it, otherwise you won't be able to adjust it.
Step 4: Almost Finished!
Then do the same things on the front and sides.