Whether you're grabbing a drink at a party, a barbecue, or in the office break room, this simple plastic cup insulation trick can keep your drink's temperature exactly how you want it, for longer.
You're obviously going to be better off with a true to form insulated cup or mug, but sometimes you don't have one around and you're forced to get creative. That's where Instructables user EurekaFactory's "InstaCool" cup idea comes in. You grab one plastic cup, a paper towel, and then a second plastic cup. Fold the paper towel hot dog style (the long ways) and wrap it around one of the cups. Then slide the second cup on as if you were going to stack them. The extra insulation slows any heat transfer; meaning the liquid in your cup will stay colder -- or warmer -- longer. You also won't have to worry about dripping condensation everywhere. This probably isn't a trick you want to abuse, since it can be wasteful, but it will help in a pinch.
InstaCool Cup: DIY Insulated Plastic Cup [Instructables]