The Slanted Lens has shared a tutorial detailing how to make one out of a sheet of inexpensive bead foam that will give you beautiful soft light. Check it out below:
The 8'x4' bead board, which you can pick up at virtually any hardware store for about $8, is pretty humongous -- unless you have a truck, I can't imagine you transporting that huge, honkin' piece of styrofoam anywhere. However, it can easily be cut down to any size you prefer. They even sell smaller sheets (4'x3' and 2'x3') for about $10 if you don't feel up to the cutting. This means that for $8, you could have multiple reflectors to use at your disposal.
Remember though, you'll want to get the kind that has the silver lining, because you'll be able to peel one side off to reveal the white bead foam, giving you a two-sided reflector with two different reflective materials.
Now, if you're thinking, "Um -- reflectors are not that expensive," you're right, but that's not the only reason Jay P. Morgan of The Slanted Lens wanted to share this tutorial with you. He also shared it because the bead board gives off a unique soft light that works really well on faces, so if you couple that with the fact that you're saving some money, it's really a win/win.
Source: The Slanted Lens