Originally Posted by luffeN
I'd like to know this as well, thx!
Take a cover in and tell them you want it to be on that type of paper, or whatever is closest.
Edit: And printing yourself can be a bit of a hassle. Printers and paper generally work best when you stick with one brand. Mixing brands can result in poor quality.
It's important to note that paper quality is key, much more so than printer quality. You don't want a cheap $30 printer from Walmart, but you don't need a super expensive printer either.
I haven't figured out what the best paper weight or type is yet, so I can't really comment on that. 8.5x11 size paper is fine, you don't need any extended sizes, just make sure you print borderless or it will be cut off. You do need bigger paper for double-wide cases though (unfortunately). My covers have used thick photo paper, but 240 gsm seems too high. Something in the 140 range is probably what is used in manufacturing.