Because her cage has open sides, Cocoa Puff gets good enough air circulation to keep her from overheating during the night and early morning. But, come late morning, she's looking a bit hot and ragged. I've started filling this old plastic vinegar bottle about 2/3 full with water then freezing it. I take it out mid-morning (when I'm here to do so) and put it in her cage. It serves as both cooler and toy, as she enjoys not only sleeping next to it, but also rolling it around her cage. Then, in the evening, I take it in, clean it off, and pop it back into the freezer until the next day. You may not have an overheated-rabbit problem, but I'd imagine there are other animals who could benefit from a similar DIY approach to a more comfortable summer. :)