A solution to keep an iPhone cool?

So you know how iPhones get hot, right? Especially the 5S, as some people in reviews have found. So I thought about a way to keep them cool. If you get a sandwich bag and fill it with water, then put it on the back of the iPhone, the heat would transfer to the water and cool it relatively quickly. Especially if the water was cold. So maybe someone could make a case or something with a tiny, highly durable bag of water (or some other coolant) that stays strapped to the back of an iPhone, that way it doesn't over heat or at least not as quickly. Does that sound like a good idea?

Yes it does.

It sounds like a lot of work, because you would have to pour out the water when it get back to room temperature or if it's warm. Plus it might not be a good idea to do that because you dropped you phone the water might spill or something. It would also look odd. Just try taking off your phone case whenever it gets hot or turn your phone off for a bit so it can cool down.

IPhones do not normally get hot.