Well, when I had frozen mice shipped, they came with a block of dry ice. It was wrapped in some sort of plastic-lined brown paper. I'd never messed with the stuff before and thought it would be cool for the kids to see...so I put it in the freezer to show them when they got home from school. By the time they did, the whole block had evaporated. I guess the stuff they had it wrapped in kept it from evaporating, even though it wasn't being stored at cold temps during shipping. :shrug: Weird stuff, that dry ice!