“We’ve got a new project for you. We’re going to replace our cold-chain account with passive packaging.”

It’s a notion I’ve heard many times before, but I will admit to having to abandon more passive packaging projects than I’ve completed – not a good win/loss ratio.

So why is passive packaging so alluring, yet such a minefield?

First, we’ll have to look at the strange alchemy that gets something from A to B before it goes off.

Cold chain, in general, comprises four essential elements:

The aim is to prevent the transfer of heat energy between the inside and outside of the packaging barrier.

What is the difference between active and passive packaging?

The fundamental difference between active and passive packaging solutions is comparable to an airplane and a glider. The airplane is more expensive in the short term but will stay aloft for as long as you can fuel the engine. The glider focuses on staying as light as possible and is acceptable to use if you only need to travel a short distance. However, it still requires something (usually another airplane) to get into the air.

Active packaging is a race to get the package to the destination before the refrigerator runs out of fuel to complete the analogy. At the same time, Passive is a race to get the package to the destination before the environment overwhelms the box.

A helpful visualization for passive might be the current best-in-class example of a temperature containment vessel – the Thermos, which comprises a flask or bottle within another. The air between the walls is sucked out, and a vacuum is formed, preventing conductive heat transfer. In addition, the glass is coated with a reflective silver mirror layer, which prevents radiative heat transfer. The thermal containment would be practically perfect if not for the opening at the top.

Not much needs to be said about actively controlled transport. It is effectively a coolroom on wheels, and with a proven track record, is still the preferred method of transporting sensitive products.

Most transport companies have the option of using refrigerated truck trailers and air freight, and the industry has become quite accustomed to the mapping and monitoring activities required. The upfront expense is high, but it excels when sending large shipments over long distances. Simple and straightforward to validate.

So what are the advantages of passive packaging?

It is excellent for moving small payloads over short distances by a dedicated courier service. It’s the transport method of choice for blood and biologicals companies as it allows them to transport quickly and with a high degree of flexibility. Applications that don’t have the luxury of waiting until the next day for a refrigerated truck benefit from passive transport.

So what have I learned from validating passive packaging?

Weight

Keeping a reasonably low weight in passive packaging can sometimes be an impossible task. During the development phase, it may become apparent that the only way to reach the destination in time is to stack more and more refrigerants adding to the transport cost.

There is an inherent limit to the amount of refrigerant shipped before it becomes impractical, both in cost and for the people handling it.

Variability

Variation in weather, the personnel setting up the package on the day, and transport delays can significantly affect the outcome.

Companies should maintain clear instructions for the configuration of shipments and train personnel accordingly.

A contingency plan for when (not if) a shipment is delayed should also be in place, which is likely to involve an active solution on standby at crucial points in the transport chain. Like the airport tarmac, for instance.

You’ll also likely need to have a separate packing layout procedure for summer versus winter. If necessary, simulations and modelling are excellent ways to determine the worst-case scenarios your product is likely to encounter. However, a model is only as good as the data you give it.

Materials

Everything from the box thickness to the quality of the refrigerant makes a difference.

Refrigerants, in particular, have a considerable variation in performance.

Gel ice is the cheapest but also performs the worst.

Dry ice is reliable but expensive and is only used for products with low temperatures. There is also the issue of safe handling.

Another option is PCM (Phase Change Materials) which are specialised materials that absorb a lot of thermal energy by transforming from one physical phase to another (i.e., solid to liquid) and as a result, they can be tailored to different temperature ranges.

What makes a PCM different from gel ice is its chemical makeup, quality and uniformity. They are usually made of paraffin waxes with a specific carbon chain length or saline solutions at a particular concentration and are reusable (but have a limit to their reuse).

Preconditioning

The majority of the passive cost comes from the amount of refrigeration you’ll need to keep on-site and the number of different size and temperature configurations. Each set temperature requires its own preconditioning chamber, which must be validated and monitored to ensure the refrigerant going into the packages is working effectively.

PCMs work better when they’re in the opposite phase to the environment they’re going up against. i.e., solid when the environment is warm and liquid when the environment is cold.

In my experience, this is the point at which most passive packaging projects are dropped as you are effectively swapping the high upfront cost of active packaging for the low but persistent ongoing cost of passive packaging. For this reason, cost should not necessarily be the reason for switching transport methods.

Specification

How strict is your specification (2°C to 8°C vs. 2°C to 25°C), and how long does your product remain stable outside of temperature? The application of passive packaging for less strict requirements is evident.

In this category, no passive solution will ever compete with active for its ability to maintain a stable and narrow temperature range for long periods.

Duration

As stated previously, passive excels over short durations – anything from 24hrs to at the very most 96hrs (and that’s being generous).

The longer the trip, the harder it becomes to justify using passive over active.

Mapping

The number of mapping points to worry about should be significantly reduced due to the smaller size of most passive shipments and the fact that you only need to map inside the payload compartment itself.

Concentrate on the top, and bottom corners of the box as these present the greatest risk and ensure to have at least one external data logger.

Conclusions

There is definitely a place in the market for passive packaging, but it presents its own unique set of complications and isn’t necessarily a direct replacement for active packaging. So before jumping in, verify the suitability of your product and not just the cost-benefit (if indeed there is any).

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