Having sold industrial paper packaging products for many years, here's my two cents.
The upholstery industry generally calls the afore mentioned product 'panel board'.
Among the general public, the terms 'panel board', 'chipboard', and 'cardboard' have all become generic words for the same type of paper product. It's actually nothing more than unrefined, really thick paper.
Do you know that we make paper the exact same way the ancient Egyptians made paper, except we use trees instead of papirus, and we use equipment that is a bit bigger that can be plugged into an electrical outlet?
I call it "panel board" because most suppliers know what I'm talking about.
Joanna, why not call it whatever your supplier calls it when you order it from your supplier, and call it whatever you think sounds most expensive when you are talking to your customers?