I see what you mean. It is possible to bend cardboard into a bowl shape, though definitely not as round as foam can make it. Though, I haven't seen a pep file where this is really needed so I haven't had trouble with it.
I'm just going to jump in here once.
**and to edit immediately, nothing on you Southpaw, but I'm speaking of tradestock cardboard (typically available boxwork in the US). I'm not challenging you on this, I just have my weight in experience of pepping, and failures from poor material choice.
Cardboard is a rigid material, just like cardstock or even paper. It is inflexible (for lack of a better word) in three dimensions. When you fold and crease it, you are simply (and beautifully) stuck in the dimensional world that us 3d modelers have to use. When you crease one direction (like paper), you are stuck finishing.
Southpaw, I'll do this politely before MS eats you alive. You really need to understand what you are talking about before suggesting things.
I've folded and built my weight in pieces, and can nearly guarantee that what you said is not true. But hey, I could be wrong too.
3 dimensional weight does not translate cleanly to cardboard, purely because of planar mathematics.
But hey, whatever. I've been wrong a gazillion times now, just ask my girlfriend.
I'm just going to assume that I'm misunderstanding you, but cardboard by necessity is a corrugated monster that is exceptionally inflexible. It has a grain like wood, and is horribly uncooperative across it's manufactured grain. It will fold and crease (at its convenience) along it's corrugation edge. If you crease and cut enough, you may create a curve.
I will say this once. You will NEVER create a dome from cardboard without tearing out corrugation, notching, or custom cutting. THE END.
THE END. Anybody who has ever tried making a dome out of cardboard can tell you this. If you've had better luck, awesome, help me. I like learning.