The Masonite with holes is usually called peg board. Same product, but different use.

If you don't find it, use several thicknesses of iron on stabilizer under a fabric base. It gives body but is not rigid. Another choice is a piece of plastic. A milk carton is too small, but perhaps you have a "dead" cutting board to cut down.

Great bag!!

You can also use balsa wood for a base.

Pretty bag.

Very nice! The colors are wonderful and wow! It's so roomy!

Very pretty bag. Looks like it can hold a lot of stuff.

Beautiful, all of my favorite colors!

Beautiful bag! I love batiks. I used those corrugated plastic advertising signs for my bag bottoms. They're easy to find, usually free. and cut very easily w/scissors or box openers.

Looks great and useful....

Such a pretty bag! I love it!