Each time I sat to pump on an international trip, I would finish by pouring all of my pumped milk into soft bendable breastmilk bags. The bags were then added to a vacuum insulated vessel to chill. Bag after bag a liquid mass of milk rode along with me throughout the day. A single ziplock of ice kept the whole day of milk production cold inside my day bag. At the end of the day, I’d lay the bags out onto sushi mats and roll them into cylinders. This step took nine months to come to. Molding the milk into a compact cylindrical shape in the freezer nearly doubled the volume of milk I could get home in one run.
Two 9.5″ sushi mats rolled six 6 oz bags of breastmilk which fit nicely into a single 11″ packing cube. In a perfect world, each packing cube would start the journey filled with clothing for a single day. As an outfit came out, two sushi rolls of breastmilk would go in. As each cube emptied, it would promptly be filled with milk and head down to the hotel freezer where it could live all week until I started packing for home. On departure day the now frozen milk chunks would be tightly nestled inside double-wall vacuum insulated vessels. Nothing but frozen milk and foam strips lived inside, minimizing air gaps so that the whole of the interior was one frozen mass.
These vessels are then packed into a cooler with two large sheet freezer packs. The combination of both a frozen environment inside the vessel and freezer packs outside of the vessel help keep the milk frozen in transit. On shorter run domestic trips this double layering approach is not always necessary. But on international journeys where the flight time plus the travel time plus a work day on either side can quickly add up to 24 hours or more, this cooler within a cooler approach is helpful.
Some of this is interchangeable, any high-density insulated cooler, any double-walled vacuum insulated vessel (though I’ve only come across two gallon-sized options), any sheet ice packs (though cooler shock is particularly impressive), any foam or filler, any bendable bags, etc.. But one thing that has been a constant is the need for a freezer. Any trip over three days starts to stretch towards the refrigerated breastmilk spoilage point, especially when you add time at home before your baby consumes the milk. Bringing home two days of chilled breastmilk still takes at least two days for your baby to drink. My girls always wanted to nurse more than usual when I returned home from a trip, further slowing the pumped milk consumption rate. Thus migrating frozen milk from a freezer in a different country to the freezer at home reduced the stress of when the milk would need to be consumed.