Craft paper. Available in 36" wide small rolls at Hobby Lobby or online with U-Line for large ones. Both are fairly cheap.

FYI: we use it regularly for layout drawings, work table covering and paint masking.

Oh, I remember those days well! My first car, a 1973 Ford LTD Brougham has some rust, so my buddy and I decided to "fix" it! We watched others do it, so we thought it would be pretty easy. Big mistake, but we learned! What went wrong?

1. We didn't remove the trim. We tried to fix the rust on the trunk and we didn't remove the trim. We sanded the rust and scratched the pot metal trim. Then we painted the area with red oxide primer (car was gold color). Of course, no taping anything, so when the primer dried, we tried to remove it with lacquer thinner. We finally gave up on cleaning up the overspray.

2. We didn't realize that the underside of the metal was in much worse condition than just the rust holes. As we poked and prodded, the holes got bigger and bigger! Some parts started out as bubbling and soon turned into holes - through both the inner and outer panel!

3. We didn't know anything about fixing the holes, so we just primered them and called it a day. Well, primer does not protect the car from rust. In fact, it absorbs water when it gets wet - which it did quite often. Soon, we saw rust marks coming through the primer!

4. Should've left it alone! That's what I can say now. We thought we were doing good work, but it looked terrible. All that red oxide primer instead of gold paint with rust bubbling under (and a couple holes in the metal)!

Fast forward to today, I've learned to tape off before painting (and sometimes detailing). I use those grocery store ads they put in our mail box. I keep a small stack in the garage and when I need to paint, they do the trick.