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How to ship breast milk so it arrives frozen
The cold chain sounds industrial. It's actually one packing list and two rules of timing, and hundreds of moms run it from their kitchen tables every week.
The short answer: a styrofoam-lined box, milk frozen flat and solid for at least 24 hours and stacked tight like bricks, dry ice or deep-frozen gel packs sitting on top, every gap stuffed with crumpled paper, and a 1 to 2 day tracked service.
Two rules of timing carry most of it: post Monday to Wednesday so nothing sits in a depot over a weekend, and send the tracking number the moment the box leaves your hands. A full, dense box stays cold; a half-empty one does not.
The packing list
- A styrofoam-lined shipping box (or a styrofoam cooler inside a cardboard box). The thicker the walls, the longer the hold – 1.5"/4 cm walls are the comfortable standard.
- Milk frozen flat and solid – bags that have been in a deep freezer for at least 24 hours, stacked tight like bricks. Tight is the secret: a full, dense box stays cold; a half-empty one doesn't. (Twenty-four hours is a minimum, not a target – the freezer clocks are here.)
- Dry ice or deep-frozen gel packs. Rough rule for dry ice: 5–10 lbs (2–4 kg) per 24 hours of transit for a mid-size box. Wrap it in paper, place it on top of the milk (cold sinks), and never in an airtight container.
- Filler. Crumpled paper in every gap. Air moves heat; paper doesn't.
- A zip bag or liner around the milk, in case a seam thaws loose in transit.
Mothers’ Milk Bank – How to Pack Your Box
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The two timing rules
- Ship Monday to Wednesday only. Milk must never sit in a depot over a weekend. This single habit prevents most thawed arrivals.
- Use a 1–2 day tracked service and send the tracking number the moment the box leaves your hands. In the US that's typically an overnight or two-day service; in the UK, tracked-24 style next-day services cover almost everywhere.
Carriers accept dry ice in ground and most domestic services with a simple label (UN1845, weight marked); check your carrier's current rule when you book. Gel packs need no labels and hold a tight box for a day easily – dry ice buys the margin for two.
Packing and Shipping Breast Milk with Dry Ice
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On arrival
Bags should be frozen solid, or at worst frosty-firm with ice crystals throughout – that still counts as safely frozen. Buyers should check contents against the listing's dates while the box is still open. On MilkMom, buyers confirm delivery within 48 hours, and a delivery that arrives thawed is a full refund – the seller's packing standard and the buyer's protection are the same system.
Common questions
How do I ship breast milk so it arrives frozen?
Styrofoam-lined box with thick walls, milk frozen solid for at least 24 hours and packed tight, coolant on top, paper in every gap, 1 to 2 day tracked service, posted early in the week. Density is the part people skip: a full box holds its cold far longer than a half-empty one.
How much dry ice do I need?
Roughly 5 to 10 lbs, or 2 to 4 kg, per 24 hours of transit for a mid-size box. Wrap it in paper and put it on top of the milk, because cold sinks. Never seal it in an airtight container. Carriers accept it on most domestic services with a UN1845 label and the weight marked.
Can I use gel packs instead of dry ice?
Yes. Deep-frozen gel packs hold a tight box for a day easily, which covers a next-day service. Dry ice is what buys you the margin for two days.
What day should I post it?
Monday to Wednesday only. Milk must never sit in a depot over a weekend, and this one habit prevents most thawed arrivals.
What if the milk arrives thawed?
Frozen solid is the standard, and frosty-firm with ice crystals throughout still counts as safely frozen. Genuinely thawed milk should not be fed to anyone: photograph it in the open box and raise it straight away. On MilkMom a delivery that arrives thawed is a full refund.
Can I hand it over in person instead?
Yes, and if the buyer is within driving distance a doorstep handoff of a cooler beats every courier on earth. The original milk round still works.