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Home > Guides > Ship frozen breast milk
Freeze the milk flat in storage bags so it stacks, pack it in a styrofoam cooler inside a sturdy box, add dry ice with the proper marking, and send it overnight: never on a Friday, since a weekend delay means it thaws. LetterAgent's shipping labels (Canada Post Xpresspost, five kilogram cap) cannot do overnight-with-dry-ice: use an express carrier that accepts dry ice.
| Step | What to do | Why it matters |
|---|---|---|
| Freeze | Freeze in breast milk storage bags, laid flat, a few ounces per bag | Flat bricks stack without air gaps, and small bags thaw only what you need |
| Inner box | Pack bags tight in a styrofoam cooler, newspaper or padding filling every gap | Air gaps are the enemy: dead air warms far faster than packed contents |
| Coolant | Dry ice on top and around, marked as required | Cold sinks: ice on top cools everything below it |
| Outer box | Cooler inside a sturdy cardboard box, taped well, labeled "perishable" | Styrofoam alone does not survive conveyor belts |
| Timing | Ship Monday through Wednesday, overnight service | Thursday shipping risks a weekend warehouse; Friday shipping almost guarantees thawing |
Regular ice packs melt into water in well under a day, and that water soaks everything. Dry ice sublimates into carbon dioxide gas instead of melting, so it stays at freezing temperatures far longer and leaves no puddle. But dry ice is itself regulated: the box needs the UN1845 dry ice marking, the net weight of the dry ice written on it, and a container that vents (never seal dry ice in an airtight box: the gas pressure builds). You will need to buy dry ice the day you ship, from a grocery store, ice supplier, or welding supply shop; it does not wait around. Wear gloves when handling it: skin contact burns are frostbite, not frost.
Often easier. Airlines let passengers carry limited amounts of dry ice in vented containers, and many parents simply pack a cooler as checked luggage rather than trusting a carrier network. If you are visiting family and need milk there, flying with a frozen cooler sidesteps the whole timing gamble. For receiving a donor shipment from across the country, though, an overnight carrier is the only option, and that is where the Monday-to-Wednesday rule earns its keep.
Food safety rules are strict here for good reason. Milk that arrives fully thawed but still cold (ice crystals present, refrigerator temperature) can be refrozen or used within a day; milk that arrives warm must be discarded. This is why the packing buffer matters more than the coolant amount: a cooler packed with zero air gaps and a generous dry ice surplus survives the "it sat in a warehouse four extra hours" scenario that wrecks tightly packed shipments. Tell the recipient to be home for delivery: a box left on a porch in summer defeats all of your packing.
A well-packed cooler with dry ice holds for roughly a day or two of transit, which is why overnight is the standard and two-day service is the outer limit for a generous pack. Every hour beyond that erodes your buffer, and summer weather cuts it further. This is also why the Monday-to-Wednesday rule matters more than the coolant choice: no amount of dry ice reliably survives a parcel sitting in an uncooled warehouse over a weekend. When in doubt, add more dry ice and pay for the faster service: the milk is worth more than the postage.
Cross-border human-milk shipments add customs and food-safety rules on top of the logistics: human milk is a regulated food product, and destination countries have their own import requirements. Milk banks handle this through established programs with documentation and cold-chain logistics, and that is the only sensible path for a large or international donor shipment. For a person sending milk to family in another province or state, keep it domestic: the rules are simpler and the transit is shorter.
Ready to ship it? Get a shipping label with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and get your label.
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