"Here Brian shows how to build a homemade cheap flash bouncer. The flash bouncer can be used to increase the size of a hot-shoe flash. The bouncer is great and very easy to build. An alternative to the bouncer is the home made softbox. Another option for building this homemade flash bouncer is to use polypropylene sheet, it is sterdier then cardboard."
Read how-to at DIYPhotography.net
Via MAKE Blog