Is it okay to check this in: a cardboard box with a styrofoam inside and store it with dry ice (< 5lbs) and frozen breastmilk (~20lbs), label it with the 'dry ice, frozen breastmilk, and fragile'? We are relocating and I absolutely need to transport my supply of milk with me.
Dry ice/carbon dioxide may be used as a refrigerant for perishables under the following limitations:
Dry ice/carbon dioxide may not weigh more than 5.5 pounds in checked or carryon baggage.
The package must be designed to permit the release of carbon dioxide gas to prevent buildup of pressure.
The outside of the container must be marked "dry ice" or "carbon dioxide solid." The net weight of the dry ice and the contents of the package must also be shown. A Southwest Airlines Dry Ice Label (WN-659) may be used to meet these marking requirements.
A few additional thoughts... I've used the sealed freezer packs before to transport frozen meat and those work well without the additional requirements of dry ice. You may also want to find a way to use an insulated bag or soft sided cooler placed inside of a suitcase. Make sure to double bag the milk to prevent any possibility of leaking.
Is your supply already frozen? If you choose against dry ice and some of the milk thaws, I’m fairly certain it’s okay to refreeze as long as each bag has some ice crystals remaining. I’ve carried on frozen and liquid breastmilk without trouble much trouble (even coming back from Mexico), places like Starbucks will give you ice. Good luck!