72-Hour Uniheat Heat Pack for Shipping Live Plants, Insects, Reptiles & Tropical Fish - Safe Temperature Control for Pet Transport, Gardening & Aquarium Use (1 Pack)

I used these to move my fish across the country, and they worked REALLY well. My tip is to ADD more to the container if you are doing the shipping/transport yourself and that way one is warming up as the other is losing heat. If you are doing 1 or 2 day shipping, these will do great for you. Make sure you don't get a "dud" though before you ship. Let it warm up 1st before sealing the container just to be on the safe side. I didn't get any duds, but I read other reviews of folks that did. They DO take a while to warm up, so be patient with them :)