Slimfold Micro [$45 + $3.95 shipping] is a highly durable thin wallet originally made for motorcycle users.
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Pro Waterproof/stain resistant
This wallet is coated in a hydrophobic material, so it won't absorb any liquid.
Pro Tested well
Slimfold Micro has been tested for durability on real pavement at speeds up to 70mph.
Con The edges bend
The parts of the wallet that aren't directly supported by cards will fold and bend.