Beersavers: You Know, For Beers
They also “help keep your beer safely identified when in clubs, bars and restaurants,” which is just hilarious.
Before you scoff, these also can work for champagne and wine bottles, so you might want to pick some up for that reason. Straight up beer protection, especially at a party, sounds kind of iffy simply because if you drop a beer by the pool and come back to it a while later, carbonation will be least of your worries. However, if you only want to drink half a beer, you can feasibly place your beer in the fridge with a Beersaver on it and go back and enjoy it later. However, as an alcoholic I cannot recommend this course of action.
They cost $7.99 for six and come in delightful colors.