I use the slotted cloths used for table flatware (silverware). Great softness (flannel feel), help prevent tarnish, easy to roll up, come in a variety of sizes. Of course can only get 6-8 folders in each roll. Can get from most any jewelry store or commonly found at flea markets, yard sales, etc. I've had very bad experiences with the usual type of knife rolls; my father-in-law had a nice collection stored in rolls, but when he fell ill and the knives were unattended for a couple years, they stained for the roll colorant and some were badly rusted. This was several years ago; perhaps the newer rolls are made of different materials. I've found the silverware rolls to be a much better alternative.
Rich