Shipping Frozen?

[Batdad]

I was wondering someone could tell me how frozen mice are shipped. I am interested because if my attempts at breeding don't work out I may have to look at buying F/T by mail order. The only thing I can get locally is pinky mice or full grown mice or rats, anything in between I am SOL. I was wondering how pinkies, fuzzies, etc. are packaged so they don't thaw and become a mess before they arrive. The smaller ones especially as they freeze and thaw so quickly.

Thanks
Bruce