You can use the phrase “paper tiger” to describe someone or something that’s not as tough as it appears to be, but you could conjure up the same image just as easily with a different pair of words. For example, “cardboard tank” seems like it could serve the same linguistic purpose. So could “cardboard Gundam” or “cardboard M16,” for that matter.
But while those might not be as powerful as their original, non-cardboard forms, they are all incredibly awesome when made out of corrugated cardboard, as proven by the creations of artist Monami Ono, who makes all those and more out of cardboard boxes from Amazon.