Perhaps, the slimmest it gets.

First guys to borrow shipping technology to slim down a wallet. The SlimFold Wallet ($20) is crafted from Tyvek — the same stuff FedEx uses for its mailing envelopes — which enables it to be 6x thinner and 5x lighter than a comparable leather wallet, while offering waterproof protection for cash, cards, and your ID. Available in four styles — bamboo, herringbone, sketch, or slate.