If you or your LO uses a PackIt lunch box or bag - does it sweat?

DD used hers for camp a few weeks this summer and every day when we got home I would take it out of her backpack and it would be sweating so much that everything was wet! It wasn't a food or drink leaking, it was just the bag sweating as the ice melts. She didn't use it last year for school, and before that was only for half day preschool. So I'm not sure if this is normal for a full day or not...