A mirror will actually absorb most of the light before spitting it back. Tinfoil isn't much better. As raven says, flat white works very well, but mylar is better.
As a graff artist, a couple cans of 2x rusto in a small space before you use it does well. In a larger space, Behr or Benjamin Moore flat white is perfect.
-spek
EDIT ^^ rusto flat white obviously
