Cutting Foam Board

I've had success using an Xacto knife and a straight edge (a metal ruler or something) to score the foamboard, then bend it along the score line and it pretty much snaps apart.

More accurately I fold it the 'easy' way to sort of complete the score, then fold it back the other way to snap it apart.

Note also that this method makes for a good fold-line n a board. Just skip the 'snap apart' portion and make sure you measure well so the fold-line is in the right place (or it folds off center and that's a little janky).

- Seth

Sharp X-Acto knives work pretty well for me. Other things I'll note are that it helps to have a really long metal straight-edge. Obviously, a straight edge helps guide the cut and make it smoother. The longer it is, the less times you'll have to reposition it, reducing the number of variations in the line. Also, X-Acto makes a little plastic knife (that uses regular X-acto blades) that has a guide on it. You can set the guide at 90 or 45 degrees. It helps ensure that the cut is vertical or angled. I find this pretty useful for making polished cuts in foam board, though it does take slightly longer than just whipping through with a regular X-Acto or utility knife.