How to Prevent Products from Freezing in 2–8°C Cold Chain Packaging

Why Is Freezing a Risk in a 2–8°C Shipment?

When buyers think about cold chain failure, they often focus on one problem:

The product becomes too warm.

But for some temperature-sensitive pharmaceutical products, the opposite problem can also matter:

The product becomes too cold.

A shipment specified for 2–8°C is not automatically protected simply because the inside of the box is “cold.”

If part of the payload is exposed to temperatures below its allowed range, the shipment may experience a cold-side temperature excursion.

For vaccines specifically, CDC states that refrigerator-stable vaccines are generally stored at 2–8°C and that liquid vaccines containing aluminum adjuvant can permanently lose potency if exposed to freezing temperatures. Product-specific storage instructions still need to be followed because vaccine requirements vary.

The packaging objective is therefore not:

Maximum Cooling

It is:

Controlled Temperature Protection

For medical shipments, that requires the container, PCM, conditioning, payload separation, packout and monitoring to work together.

For an overview of the complete medical cold chain system, see our Pharmaceutical & Medical Cold Chain Packaging Solutions.

1. Frozen Cooling Packs Can Create Local Cold Spots

One of the most common risks occurs when a cooling element leaves a freezer at a temperature far below the product's acceptable range.

Imagine a 2–8°C pharmaceutical carton packed directly against a conventional cooling pack that has just been removed from a –18°C freezer.

Even if the average internal air temperature later remains within 2–8°C, the product surface immediately beside the frozen pack can experience a very different thermal condition.

This is called a local cold spot.

The risk depends on:

• cooling material;
• conditioning temperature;
• contact area;
• payload sensitivity;
• barrier thickness;
• packout geometry;
• duration of contact.

This is why a single sensor placed in the center of the box cannot always tell you what happened at the coldest product location.

For freeze-sensitive applications, buyers should evaluate the coldest likely payload position, not only the average internal temperature.

2. Select the Cooling Material for the Required Temperature Range

Cooling materials should be selected according to the product requirement—not according to which pack becomes coldest.

Typical options include:

• frozen gel packs;
• rigid ice bricks;
• eutectic plates;
• temperature-specific PCM.

For general food transport, deeply frozen gel or water-based packs may be entirely appropriate.

For a temperature-sensitive 2–8°C pharmaceutical shipment, a PCM designed around an appropriate temperature profile may provide a more controlled starting point.

PCM, however, does not automatically guarantee 2–8°C performance.

The complete configuration still depends on:

PCM Profile + Quantity + Conditioning + Insulation + Payload + Packout + Ambient Conditions

Different PCM temperature profiles and rigid/flexible formats are discussed in our Pharmaceutical PCM Solutions.

3. Conditioning Matters as Much as PCM Selection

Selecting the correct PCM is only the first step.

The material must also enter the package in the appropriate condition.

Depending on the PCM formulation and validated procedure, preparation may involve:

• freezing;
• refrigeration;
• controlled pre-conditioning;
• equilibration;
• confirmation of phase state before packing.

The same six PCM panels can behave differently if one shipment uses correctly conditioned PCM while another uses panels taken directly from an unsuitable freezer temperature.

This is why a professional packout instruction should not simply state:

“Add six PCM packs.”

It should define:

Which PCM?

How is it conditioned?

At what temperature?

For how long?

What condition should it reach before packing?

For repeatable pharmaceutical distribution, these operating instructions are part of the packaging system.

4. Avoid Direct Contact When the Product Requires Separation

For some configurations, placing very cold cooling elements directly against the payload can increase cold-side exposure.

A packout may therefore use:

• corrugated dividers;
• foam separators;
• molded payload chambers;
• trays;
• controlled air gaps;
• other thermal barriers.

Their purpose is not simply mechanical protection.

They can also help regulate the heat-transfer path between the cooling element and the product.

A simplified structure may look like:

PCM → Thermal Barrier → Pharmaceutical Payload

instead of:

PCM → Direct Product Contact

 

Whether a barrier is required—and what kind—depends on the product, PCM and tested packaging system.

Simply inserting arbitrary cardboard around the product should not be treated as a validated freeze-protection strategy. WHO vaccine guidance has specifically cautioned that simple wrapping materials are not necessarily effective protection from fully frozen ice packs for freeze-sensitive vaccines.

The configuration needs to be developed and tested as a whole.

5. Pay Attention to All Six Sides of the Payload

Packout design is three-dimensional.

Cooling elements may be positioned:

• on the bottom;
• on side walls;
• on the top;
• around four sides;
• around five sides;
• around all six sides.

More PCM coverage does not automatically mean better protection.

Consider two risks.

Too little coverage

Some regions can warm too quickly.

Excessively cold or poorly positioned coverage

Some payload locations may become too cold.

The objective is to find a balance between:

Hot-Side Protection ↔ Cold-Side Protection

For example, a six-sided PCM configuration may offer good thermal coverage in one system, but its conditioning and payload separation still need to be appropriate.

This is why packout development should answer both:

How much PCM is required?

and:

Where should that PCM be positioned?

Our guide From Box to Packout: Why Cold Chain Performance Depends on the Complete System explains this relationship in more detail.

6. Winter Routes Can Create a Different Freeze Risk

Cold-side risk does not come only from cooling packs.

The external environment itself can also cool the payload.

Consider a pharmaceutical shipment traveling through:

• sub-zero outdoor temperatures;
• winter airport handling;
• cold delivery vehicles;
• unheated warehouses.

During summer, the insulation system is primarily slowing heat entering the package.

In winter, the heat-flow direction can reverse.

The same package therefore needs to be evaluated for both:

Hot Ambient Exposure

and

Cold Ambient Exposure

where relevant.

This is one reason thermal qualification may use separate hot and cold profiles rather than one constant room-temperature test.

WHO also requires vaccine cold-chain devices in relevant categories to demonstrate protection from freezing; for certain vaccine refrigerators, temperatures of 0°C or lower in the vaccine storage area are not accepted.

The lesson for packaging buyers is straightforward:

A successful summer packout should not automatically be assumed to provide adequate winter freeze protection.

7. Payload Starting Temperature Matters

A 2–8°C shipment should not be treated as a system in which the packaging must cool a warm payload down to its target range unless the system was specifically designed for that purpose.

For example:

Shipment A

Payload begins at approximately 5°C.

Shipment B

Payload begins at approximately 20°C.

These two systems have very different initial thermal loads.

The opposite problem also exists.

If the payload itself begins close to the lower end of the permitted range and is then placed beside very cold PCM, the margin before a cold-side excursion can be smaller.

For thermal testing, the payload starting temperature should therefore be documented.

8. Sensor Placement Is Critical for Detecting Freeze Risk

One temperature logger in the center of the box may miss the coldest location.

During packout development, useful measurement positions may include:

• payload center;
• payload near a PCM panel;
• near the top;
• near a side wall;
• likely warm location;
• likely cold location.

This does not mean every routine shipment needs many loggers.

Development testing and operational monitoring are different purposes.

During development, multiple sensors help identify:

Where are the hot spots?

and equally importantly:

Where are the cold spots?

CDC's vaccine storage guidance similarly emphasizes temperature monitoring as the means of knowing the actual storage temperature rather than relying on thermostat settings alone.

For cold chain packaging, the same principle applies:

Measure the product environment—not merely the apparent coldness of the box.

9. Do Not Judge Performance from the Average Temperature Alone

Consider five sensors inside a shipment:

Sensor	Result
Center Payload	5.1°C
Upper Payload	6.0°C
Side Payload	4.2°C
Near PCM	1.0°C
Opposite Side	6.4°C

An average of these temperatures could appear acceptable.

But one payload location has already fallen below 2°C.

This is why a thermal report should not only ask:

“What was the average temperature?”

It should ask:

Did every critical payload location remain within the required acceptance range?

This is particularly important when assessing freeze-sensitive products.

10. A Practical Freeze-Protection Packout Development Process

A practical development sequence is:

Step 1 — Confirm the Product Requirement

Define the exact acceptable temperature range and any freeze sensitivity from the product specification or manufacturer.

Step 2 — Define the Payload

Record dimensions, weight, quantity and starting temperature.

Step 3 — Select the Insulated Container

Choose the appropriate EPS, EPP, PU, VIP or composite system.

Step 4 — Select the Cooling Profile

Choose gel, ice bricks or PCM according to the required temperature range.

Step 5 — Establish Conditioning

Define the cooling element preparation procedure.

Step 6 — Design Payload Separation

Determine whether direct contact is acceptable or a thermal barrier is required.

Step 7 — Design the Packout

Position coolant around the payload according to expected heat-flow paths.

Step 8 — Identify Hot and Cold Measurement Points

Do not monitor only the easiest location.

Step 9 — Test Hot and Cold Conditions

Where relevant, consider both summer and winter transport challenges.

Step 10 — Adjust and Repeat

Change PCM quantity, conditioning or layout when the test identifies excursions.

This approach treats freeze protection as part of system design, not as an afterthought.

Common Causes of Freezing in 2–8°C Packaging

1. Using deeply frozen packs directly against the payload

This can create severe local cold exposure.

2. Incorrect PCM conditioning

The right PCM used in the wrong starting state can still change system behavior.

3. Too much coolant in the wrong locations

More thermal capacity is not always better.

4. No thermal separation

Sensitive products may be exposed directly to very cold surfaces.

5. Ignoring winter ambient conditions

External cold can become the dominant thermal challenge.

6. Monitoring only the center of the box

Cold spots close to PCM may remain undetected.

7. Changing the payload without reassessing the packout

Different payload mass and geometry can change thermal response.

What Should Buyers Ask Their Packaging Supplier?

For a 2–8°C freeze-sensitive shipment, ask:

1. Which PCM or cooling material is being used?
2. What is its intended temperature profile?
3. How should it be conditioned?
4. Can coolant contact the product directly?
5. Is a thermal separator included?
6. How much PCM is used?
7. Where are the PCM panels positioned?
8. What payload was used during testing?
9. What was the starting payload temperature?
10. Were both hot and cold ambient conditions evaluated?
11. Where were temperature sensors positioned?
12. What were the warmest and coldest payload temperatures?

These questions provide much more useful information than simply asking:

“Can your box keep 2–8°C for 72 hours?”

How Glacier Spark Approaches 2–8°C Freeze Protection

For project-based pharmaceutical packaging, Glacier Spark evaluates cold-side risk together with overall thermal performance.

Depending on the shipment, the project can include:

Container Selection
EPS, EPP, PU or VIP-based insulated packaging.

PCM Selection
Temperature-specific rigid or flexible PCM formats.

Conditioning Guidance
Preparation requirements for the selected PCM.

Payload Separation
Internal chambers, separators or barriers where appropriate.

Packout Development
PCM quantity and positioning around the actual payload.

Monitoring Layout
Measurement positions designed to identify both warmer and colder locations.

Thermal Evaluation
Packout adjustment according to agreed payload and ambient conditions.

For vaccine-specific applications, see our Vaccine Transport Solutions.

The objective is not simply to keep products cold for as long as possible.

It is to maintain the required product temperature without unnecessary hot-side or cold-side exposure.

Frequently Asked Questions

Can a frozen gel pack damage a 2–8°C pharmaceutical product?

It can create temperatures below the target range if the product is freeze-sensitive and the configuration allows excessive direct cold exposure. Suitability depends on the specific product and tested packout.

Is +5°C PCM better for 2–8°C shipping?

A PCM around an appropriate phase-change temperature may be useful in some 2–8°C systems, but the nominal PCM temperature alone does not qualify the package. Insulation, conditioning, quantity, payload and testing still matter.

Should PCM touch pharmaceutical products directly?

That depends on the PCM, conditioning and product requirement. Some systems use direct contact; others require controlled separation. The tested configuration should define this.

Does more PCM reduce freezing risk?

Not necessarily. More coolant can increase cooling capacity but may also increase cold-side exposure if it is incorrectly conditioned or positioned.

Should 2–8°C packaging be tested in winter?

If the intended distribution route can experience low ambient temperatures, cold-season conditions should be considered during system qualification.

Where should the temperature logger be placed?

Routine monitoring requirements depend on the shipment and procedure. During development, multiple locations may be evaluated to identify both likely hot and cold spots.

Conclusion

Preventing freezing in 2–8°C cold chain packaging requires more than choosing a box that “stays cold.”

The complete system must balance:

Cooling Capacity + Freeze Protection

That requires the correct combination of:

PCM Selection → Conditioning → Payload Separation → Packout → Ambient Conditions → Monitoring

For freeze-sensitive products, the coldest payload position can be just as important as the warmest one.

The goal is not:

Keep it as cold as possible.

The goal is:

Keep the actual product within its required temperature range throughout the intended shipment conditions.

Need Help Developing a 2–8°C Packout?

Send Glacier Spark:

Product Temperature Range + Payload Dimensions + Payload Weight + Transit Time + Route + Ambient Conditions

We can help evaluate the insulated container, PCM profile, conditioning direction, payload separation and packout configuration for further thermal testing.