I shipped a dozen eggs (for eating) to my brother in San Diego the week before Christmas. Weather was wicked up here in Minnesota with night time temps dipping below zero, not figuring wind chill. I put a 24 hour heat pack in the box (away from the eggs) and sent them Priority with USPS. They got there in 2 days and were all fine. I got my heat packs through someone that sells them for the aquarium hobby for shipping fish and live plants.