Well, if you making a cardboard armor it wont be as good as a pep armor! But if you dont have much time and just want a smilar like armor cardboard is great! I tried to make a cardboard armor and the only thing you have to do is cutting a pice as exemple a chest plate and if it's good you can add details and make the backpack! But if it's bad (chest plate) you can just remake it untill you got it like you want it!