Black card stock.
BTW...Isn't it nice to be able to call a company...like Ross..., talk with 'Mr. Big', Steve, who is there and cares to help you, and gives you a solution...that works?? Better than a sleeping pill.
Steve is awesome.
I actually went to his factory a couple of years back and he gave my wife and me the grand tour.
I have also spent a lot of money with him, and I believe his equipment is worth every cent.
Now, I mostly email him, and let him respond at his leisure.
I always get a response within a day