Why does my cooler sweat, and is it broken?

Your cooler sweats because of condensation — cold surface meets warm, humid air. It’s not broken; physics is just doing its thing. To reduce sweating, put it in the shade, open it less, wipe it dry before bringing it inside, and pre-cool it with ice packs. A rotomolded cooler helps, but even a Yeti sweats in high humidity. A towel under the cooler solves the puddle.