Ferrets are always cool animals, but when the temps get up they need help not overheating.
I heard about an ingenious way to help keep your fuzzys cool on hot days, so I thought I'd pass it on:
Get some unused ceramic tile. 12 x 12 floor tile is ideal, but you can work with anything.
Rotate them into the freezer, and the cage. Keep one on the cage floor so that the ferrets have someting very cool to flat-ferret on and cool off. You may want to put a thin cloth (receiving blanket, etc.) over it to make it not so cold for them.
That's it!
I've got a couple of kids right now cooling off on some leftover floor tile from a project.