I purchased the 12 can size in order to transport breast milk during a 6 day trip out of town for work. Every day I brought this cooler to the convention with me along with a gallon sized ziplock bag full of ice. After pumping I’d store the milk in the cooler. I was away from a fridge about 8 hours each day but the cooler kept everything very cold. In fact, at the end of the day the ice would still be mostly unmelted in the ziplock bag, and the milk would be cold.At the end of the trip I packed all of the milk into my AO Cooler along with another ziplock bag full of ice. I was able to freeze some of the milk before flying and when I got home about 8 hours later only two 6oz bags of milk had slightly started to thaw. The rest was still frozen solid. Most of the milk I transported was not frozen and the sturdiness of this cooler prevented any bags from opening, even when jostled by other carry-on luggage in the overhead storage bin on the airplane. All of the milk was extremely cold when I made it home. If you are going to be expressing breast milk away from home more than 6 days, I might recommend getting the 24 can size instead. I could only fit a very little bit of ice in the cooler on my way home with the 12 can size that I purchased.This bag made the very stressful process of transporting and storing breast milk while away from home as painless as possible. The 12 can size is large – don’t expect it to easily fit underneath the seat in front of you on an airplane. But it is sturdy, well-made, and can protect your precious cold items during long periods of time away from refrigeration.As a side note – when I got home I accidentally left a ziplock bag full of ice in my AO Cooler for over a day before I realized it was there. The cooler was unzipped that entire time, and when I pulled the bag out of the cooler, the ice had melted but it was still extremely cold. The insulation in these coolers is pretty amazing.