Why lyophilised peptides ship at room temperature: cold packs, dry ice and the cold chain

Freeze-dried (lyophilised) peptides are stored in a freezer, so it can seem odd that they arrive in an ordinary parcel with no ice. The reason is that a dry powder is far more stable than a peptide in solution. A few days at room temperature makes little difference to most freeze-dried peptides. This guide explains why, what cold packs and dry ice do, what the "cold chain" is, and what to do when a parcel arrives.

Terms are defined in the glossary.

Why a dry powder travels well

Most of the ways a peptide breaks down need water. Hydrolysis splits the chain using water. Deamidation and many oxidation reactions run much faster in solution, where molecules can move and meet each other. See shelf life and stability for the main reactions.

Freeze-drying removes most of the water. What is left is a dry, glassy solid in which molecules can hardly move. Reactions still happen, but slowly. That is why the powder lasts for years in a freezer, and why a few days at room temperature uses up only a tiny part of that shelf life. See what lyophilisation is for how the dry cake forms.

Cold storage is still the right choice for the long term. Chemical reactions slow down as temperature drops, so a vial kept at −20 °C changes far less over months than one kept on a shelf. The point is that the time in the post is short compared with the time in storage.

There are exceptions. Some compounds are less stable, and a parcel left in a hot vehicle or in direct sun can get much warmer than room temperature. Each product page lists the recommended storage condition for that compound.

What cold packs do

A cold pack is a sealed pouch of gel or water, frozen or chilled before packing. It keeps the inside of a box cool for a limited time, usually hours to a day or two, depending on the insulation and the weather.

For freeze-dried powder sent by post, cold packs add less than they seem to:

• They warm up before most parcels arrive. A two-day delivery often outlasts the pack.
• They can add moisture. A cold pack sweats as it warms. If water gets into the bag, or if a cold vial is opened in warm air, moisture can reach the powder. Freeze-dried peptides take up water from the air easily. See hygroscopic powders.
• They aren't allowed in the post as a coolant. Royal Mail doesn't accept frozen water as a cooling method (Royal Mail).

Cold packs matter more for things that are already in solution, or that spoil within hours at room temperature.

What dry ice is

Dry ice is solid carbon dioxide. At normal air pressure it doesn't melt. It turns straight from a solid into a gas, at about −78.5 °C. That makes it useful for keeping things frozen in transit without leaving any liquid behind.

Labs use dry ice to ship frozen samples, such as solutions, enzymes and cell lines, which would be damaged if they thawed. It needs care:

• It gives off a lot of gas. A sealed, airtight container can burst. Packages are designed to let the gas escape.
• It can build up carbon dioxide in a closed space, such as a car or a small room.
• It burns skin on contact. Handle it with insulated gloves.
• It is a regulated dangerous good for air transport, and many carriers restrict it. Royal Mail doesn't accept it as a coolant (Royal Mail). Couriers that do accept it need specific packaging and labels.

For a freeze-dried powder, dry ice adds cost and handling risk with little benefit.

What the cold chain is

The cold chain is an unbroken series of temperature-controlled steps, from where something is made to where it is used. Each step, including storage, transport and handover, keeps the product within a set range, often 2–8 °C or frozen. Temperature loggers record that the range held throughout.

A cold chain is essential for materials that degrade quickly when warm, such as many proteins in solution and biological samples. A freeze-dried peptide doesn't need an unbroken cold chain for a short journey, but it does need sensible storage before and after.

When a parcel arrives

1. Put the vial in storage promptly. Use the temperature on the product page, usually −20 °C, sealed and away from light. See how to store lyophilised peptides.
2. Don't open the vial while it's cold. If you need to open it straight after taking it out of the freezer, let it reach room temperature first, ideally in a sealed container with a desiccant. This stops moisture condensing on the powder.
3. Check the vial. The seal should be intact. The powder is often a small white cake or a thin film, and may look like very little. See why lyophilised vials look nearly empty.
4. Note anything unusual. A cake that has visibly melted or shrunk into a sticky residue, a discoloured powder, or a broken seal is worth reporting with the lot number. The lot number links the vial to its COA. See lot numbers and batch numbers.

How we ship

We ship UK orders at ambient temperature by Royal Mail Tracked 48, or Tracked 24 for express, with each vial sealed in a bag. Each product page lists the recommended storage condition for that compound. Every lot has its own COA, published on the product page and on that lot's own page. See Quality.