640 gsm paper

They make teflon folders now, too, which are highly regarded. They are inexpensive. A good, heavy metal ruler is a good thing to have, if you can get one for the size you need. Then it won't slip as much, as it does take some muscle to hold the ruler down to keep a clean scoring line since you have to go back and forth a few times. There are now deckle-cutting rulers with bumpy edges (and some are metal) but you would want to use it only at the very last tear with 300lb/640gsm paper. It isn't as beautifully diaphanous as a proper papermakers' deckle, but does have a nice character of its own.