OK, so it’s not, actually. Bulletproof, that is. But with 3/32″ aluminum sheet covers, nickel-plated steel piano hinges, and all-riveted construction, it’s a damn sight tougher than just about any other 3-ring binder you’re likely to encounter in the wild. Especially those crappy cardboard-shrinkwrapped-in-vinyl models most of us had/have to make do with in school.
(And no, you don’t have to use an old road sign to make yours, but it does confer serious style points. Just make sure it’s not stolen, please. They need the road signs, you know, on the roads.)