sturdy paper?

[oversoul.livejournal.com]

I'm wondering what kind of paper people normally use to make gift boxes and gift bags (not kraft sack though)? I'm looking for something sturdier, similar to posterboard, or maybe even bristol...? But not thick enough so that it becomes difficult to fold...

Thanks in advance if you can help me figure this out! :) If you guys have any tips for making sharp, crisp folds, that would come in handy too. :)