LetterAgent
Mail physical letters by just asking your AI assistant.
Home > Guides > Shipping with a cold pack
Freeze gel packs solid, line the box with insulation, place the cold packs around the item, and seal everything in a leak-proof bag. Plan for the packs to outlast the trip with plenty of time to spare, and drop the parcel off as late in the day as the carrier allows.
Gel packs win for most parcels. Plain ice melts into water that soaks labels, softens cardboard, and pools at the bottom of the box. A sealed gel pack stays contained as it thaws, and the gel itself holds cold longer than the same weight of ice because it melts more slowly. Reusable gel packs are also easy to freeze flat, which matters: a flat pack stacks neatly against the item, while a lumpy bag of cubes leaves air gaps where warm air collects. Keep a few packs in the freezer at all times if you ship chilled goods more than once, since a pack pulled from the freezer an hour before packing is not the same as one frozen solid overnight.
Think of the cold pack as a clock. The trip starts the moment the parcel leaves your hands, not the moment the carrier scans it, and it ends when the recipient opens the box, not when the tracking page says delivered. A parcel left on a sunny porch for hours after delivery keeps warming, so tell the recipient when to expect it and ask them to bring it inside right away. Build in slack for a missed connection or a weekend hold: if the trip should take two days, pack enough cold to last three. Summer heat, a long rural route, and a parcel sitting in a hot vehicle all shorten the clock, so the same pack that works in April may fail in July.
| Packing choice | What it does |
|---|---|
| Gel packs frozen solid overnight | Longest cold life, no free water as they thaw |
| Insulated box liner or foam panels | Slows heat entering the box from every side |
| Cold packs on all sides of the item | Keeps the temperature even instead of cold on one side only |
| Leak-proof inner bag | Contains condensation and any pack that splits open |
| Void fill on top | Stops warm air from sitting in empty space above the item |
Line the box first. Foam panels, a reflective bubble liner, or even a thick layer of crumpled paper around the inside walls all slow heat transfer, and a liner is cheap insurance compared with a spoiled shipment. Next, seal the item itself in a zip bag or shrink wrap: condensation forms on cold surfaces, and a wet label or soggy carton hurts even if the contents survive. Put a frozen pack on the bottom, set the item on it, then pack frozen packs around the sides and one on top, since cold air sinks and the top pack cools the air above the item. Fill every remaining gap with crumpled paper so nothing shifts, then close the inner bag around the whole bundle before you seal the outer box.
Dry ice is far colder than a gel pack and suits frozen goods that must stay frozen, but it comes with rules gel packs do not. It gives off carbon dioxide gas as it sublimates, so the box must vent and must never be sealed airtight. Carriers ask for the dry-ice weight marked on the box, and some services cap how much a parcel may carry. Dry ice also burns skin on contact, so handle it with gloves and keep it away from the item itself with a layer of paper, or delicate goods can freeze-crack. For chilled but not frozen goods, gel packs are simpler, safer, and usually enough. If your goods must stay frozen solid for days, dry ice is the honest choice, and you should confirm the carrier's dry-ice rules before packing.
Leaks come from two places: condensation on cold surfaces and a pack that splits under pressure. The inner bag handles both, as long as it is truly sealed and not just folded shut. Double-bag anything liquid or anything that would be ruined by damp, and put the label on the outside of the box, never on the inner bag. Tape the outer box with wide packing tape in an H pattern, and mark the box with the recipient's address on more than one side in case one label gets wet. If the parcel contains food, medicine, or anything perishable, check whether the carrier accepts it at all: some services refuse perishables, and a cold pack does not change that rule.
Timing is half the packing. Drop the parcel off as late as the carrier's cutoff allows, so it spends the night moving instead of sitting in a warm depot. Avoid shipping chilled goods on a Friday unless the service truly moves on weekends, or the parcel may sit until Monday. In Canada, a LetterAgent label covers Xpresspost parcels up to five kilograms within Canada, so weigh the packed box with its gel packs included: frozen packs are heavy, and a box that was under the limit empty can cross it once packed. Keep the tracking number and send it to the recipient with the expected arrival window, so the box gets opened promptly at the other end.
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.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
Need help? Ask your assistant: it can check a job's status any time. If it ever can't handle something: hello@getletteragent.com