It's fine to use without warming it up during summer application, but it will be slightly more difficult to apply. I typically dunk my bottle in the sink, close the stopper, and just let warm water run over it for a minute or two and it's ready to rock.
While it was mentioned before; I've had outstanding success with Collinite 845 Liquid Insulator wax. Ridiculously easy to apply and remove with little effort. I typically apply it by hand with a microfiber applicator.