PA Blank Framing Mats are a good place to begin, especially if you have an odd size picture that you'd like to mat, you can cut the interior dimensions yourself and save some money. You can also use them as a sturdy backing for a framing "sandwich" and even use then as a base for other art projects. Of course they are acid free, but not suggested for use in Conservation Framing. Solid pieces of mat board with no openings. 5"x 7" White Core Black 5pc- Measurement is exterior dimensions. Black surface with a White core.