A University of Washington study demonstrated condensation build-up on the outside of a beverage can produce more heat than the surrounding air.
The study concluded that a can of beer could warm up twice as quickly in humid weather than in dry heat conditions.
“Probably the most important thing a beer koozie does is not simply insulate the can, but keep condensation from forming on the outside of it,” said Dale Durran, a University of Washington professor of atmospheric sciences.
A world-record dew point of 35 °C occured in Dhahran, Saudi Arabia during July 2008, where the air temperature was 43 °C – under those conditoins, the study calculated that the condensation deposited in five minutes on a can of beer initially near 0 °C would warm the beer by about 9 °C.
An air temperature high of 36.8 °C hit Toronto, ON last summer during July, according to the National Climate Data and Information Archive.