“HOW IT WORKS”
Most people think these items work by insulating the can, thus protecting it from the ambient heat.
They do insulate, yes, but this isn’t the main reason they keep your drinks cool.
When moist, warm air touches your beer can, water condenses on it. This means that the water vapour in the air has just dumped some heat energy into your beer and warmed it ever so slightly. (Just in the exact opposite way your freezer cools things by evaporating a liquid)
So OK, the Koozie does insulate your can, but more importantly it protects your can from condensation, which will warm up your beer much faster than just being in a warm environment.
Look beyond the relatively thin insulative layer and think of all that horrible, drippy condensation your blocking from dumping heat into your coldie!!