Cutting foamcore boards

I have been a lurker in these forums for about a month now. I recently started cutting my own mats and backing boards and I had a problem last night while cutting a foam core backing board. I don't seem to be able to cut it without "clumping" the material or tearing it. The method I used was: mark the line I want to cut with a pencil, use a ruler as a support and cut the board with a utility knife. Does anyone have any tips on how to cut it correctly?

Thanks!
Shesh

Try a fresh blade. If that doesn't work, switch to an X-acto knife with a fresh blade.

A fresh blade; I use a utility knfe, one of those with the longer blade that comes out of the handle, yeah, the el cheapo model. But for me, I set the blade at a 45° angle at the top of the cut, and go through the entire thickness of the board in one pass. I've had much better suscess with this method as opposed to "scoring" with several passes.

And use a backing board (an old scrap of foam core) so the tip of the blade, dulled by passing over whatever hard surface you use, is not actually cutting the board itself.

I just cut 20 40x32 boards down to 16x20, 20x24, and 24x28 using my new Logan 750 SimplexPlus. Took about 30 minutes. If you are going to cut much, get one of these! They are only $230 or so (I got mine from http://allartsupplies.com ) and it has brought joy into cutting mats. Merry Christmas! Merry Christmas, Everyone!