Thermal blankets, covers, shrouds and quilts… What’s the difference?
Thermal Covers / Skins / Hoods / Caps: Thin (usually single layer) and low cost, designed for single trip use. Primarily a reflective material protecting against direct sunlight during temperature spikes. Usually supplied in preformed sizes. Also known as thermal pallet hoods, wraps, skins etc.
Thermal Blankets / Quilts: Often thicker insulation with robust outer materials, designed with more durability for repeat use and closed loop operations. May provide higher protection against convection temperature threat (see ‘Temperature Threats’ below). Usually supplied in preformed sizes.
Shroud: A single rectangular piece or layered piece of materials designed to lie over the goods to be protected.
Temperature Control vs. Temperature Protection – What’s the difference?
Typically, thermal blankets etc. do not ‘hold’ temperature between limits, they are designed to ‘slow down’ temperature exchange, to allow more time to move between risk points. This is in contrast to TCP (Temperature Controlled Packaging) that utilises insulating and phase change materials to hold temperature for a validated duration (e.g. 72hrs). For this reason, thermal covers are considered as ‘temperature protection’ rather than ‘temperature control’ packaging (TCP).
What is the performance expectation of thermal blankets / covers etc?
Thermal blankets will generally allow passage of temperature exchange as soon as there is a difference between the inside and outside temperatures. The rate of change will depend on many variables so it’s very difficult to predict the performance. These variables include:
1. Load Size: Size of load mass (the larger the load mass, the slower the temperature change e.g. an air cargo PMC pallet will have better thermal performance than a Euro skid pallet).
2. Product Mass: How condensed the load mass is (a barrel of liquid will keep better temperature than a pallet of small bottles of liquid with lots of packaging between)
3. Product Mass Type: The type of load mass will impact performance i.e. liquid, powder and solids will react differently.
4. Packaging Configuration: Type and design of packaging (bottles of liquid in shrink wrap packs will be more exposed than well packaged liquid protected by polystyrene and cardboard)
5. Strength of Direct Sunlight: The balance between ambient air temperature and direct sunlight (pallets exposed to similar levels of sunlight can perform quite differently if the ambient temperatures vary.
6. Temperature Differential: Generally, a higher temperature differential between the pallet load and ambient results in an increased rate of thermal change. A pallet exposed to harsh sunlight in Dubai may rise 5-10°C even when protected by a thermal blanket or cover. European sunlight the same pallet may only rise by 3-6°C in the first hour. In Canada, the opposite can happen in harsh cold with windchill.
7. Exposure Duration: During subsequent one hour periods, the temperature will rise or fall less than the previous (at the same ambient condition).
Do covers/blankets work the same in cold weather?
What are thermal blankets and covers best suited for?
It often comes down to COST! When the majority of a transit route is within safe operating temperatures, companies are obviously reluctant to spend more than necessary on thermal protection.
Short duration temperature spikes during the supply chain threaten temperature integrity and product efficacy. Occurrences are normally during loading and off-loading (truck, ship or aircraft), cross docking and adverse warehouse conditions.
These durations can be quite short (no more than a few hours) and can be protected against with cost effective thermal covers.
Typically, the nature of the protection lends itself well to ambient pharmaceuticals that have wide temperature limits proved through stability data. Examples:
2-25°C where the goods don’t start too close to the temperature limits (e.g. don’t expect goods at 22°C to keep under 25°C when exposed to 4hrs of tarmac time in Dubai – if they come out of the aircraft at 5-10°C, they may stand a chance).
15-25°C where the ambient isn’t too aggressive (note that there is often a desire to protect between 15-25°C even when there is tolerance to allow higher and lower temperatures, this will impact the cost as it’s far more challenging to protect between 15-25°C with passive insulation).
25°C due to ‘storage’ rules, but these can sometimes be waivered during transit, allowing temporary wider tolerances).
2-40°C is the most common tolerance with normal ambient goods, and should be ideal for thermal cover protection.
2-8°C either for secondary protection (e.g. in active containers, or to cover TCP pallet shippers) or if used as primary protection, for VERY short durations of exposure, definitely less than 1 hr – less than 20 minutes if harsh ambient environment.
Are thermal blankets / covers easy to fit and remove?
Yes, they usually come preformed and fit over the pallet like a hat, then sealed into place using tape or a rubber ‘Pallet Band’. This should take no more than a minute or two. Removal should be just as quick.
The only exception is where rolls of insulation are used. This can take two people up to 10-20 minutes if not using the preformed solution.
What difference does a thermal base make?
If operationally possible, adding a thermal base on the pallet before loading the freight will provide an improvement in thermal performance, especially when protecting against cold ambient temperarures.
Having the load fully enclosed will have the following benefits:
- Reduce ambient air exchange (convection) temperature threat
- Reduce influx of rising air from hot airfield tarmac
- Create a sealed unit to prevent contamination
What if a thermal base can’t be fitted?
Will adding a second cover double the performance?
Will using gel packs or phase change materials help performance?
Yes, quite considerably if done effectively. This is particularly effective when shipping a low mass product that can change temperature easily and would benefit from the extra mass.
The main considerations would be practicality, operational and cost. Strips of gel packs would be placed over the top of the built pallet before fitting the thermal blanket / cover.
When is the best time to fit thermal blankets during the shipping process?
Covers / blankets should be fitted at the point where the freight is at the correct temperature. The covers should also be at the same temperature.
Fitting warm covers outside of the controlled temperature area will have the effect of warming up the freight (like a coat), so should be avoided.
How do you assess if covers or quilts / blankets will provide sufficient protection?
- Define the temperature limits of the product being shipped.
- Often there may be ‘desired’ temperature limits but the product has stability data to allow broader limits, e.g. Ideal product temperature limits: 15-25C but allowable 2-30C for no more than 24hrs.
- Assess the supply chain route and identify likely risk points where the temperatures exceed the product temperature limits. Establish the higher / lower expected ambient temperatures AND the duration the shipped goods are likely to be exposed to these temperatures.
- For example – Risk Point: Abu Dhabi Airport (transit point – ramp time). Ambient Temperatures: 40C / Direct Sun Temperature 60C. Duration of Exposure: up to 2hrs.
- Ideally, each route should be assessed and managed accordingly and given a risk profile depending on the season, e.g. Green, Amber, Red.
- Request performance data information from vendors that indicate whether any solutions can protect goods from the likely threat.
- Selecting the correct solution for the company is often about finding the balance between cost and performance.
- Thermal blankets and covers can provide adequate thermal protection for the durations required whilst being affordable. With a well managed supply chain, there is often little need to invest in solutions that will provide protection for the whole journey, when much of the duration is within safe temperature limits. For example, there may be no need for a 72hr shipper, when the only threat or risk point in the supply chain is a 2-4hr window at each airport during aircraft loading and unloading.
- With goods that are of high value or operationally time critical, we would recommend using Temperature Controlled Packaging, or Active Containers to be certain of maintaining safe temperatures.
Ground handling teams can confuse thermal covers for permanent protection and decide to leave pallets on the tarmac thinking it’s protected. Ensure that your ground handling colleagues give priority to temperature sensitive freight whether it’s covered or not.
The Shippers Dilemma: Cost vs. Quality
Understandably, there is resistance for shippers to pay any additional costs for ambient goods that have historically been sent through standard freight lanes. With more ambient goods being shipped with temperature limits, it’s a risk to allow sensitive freight to be exposed to delays on the tarmac. If there is a requirement for temperature control, there is naturally a cost to providing this protection, whether it’s through priority service, or thermal protection, or both.
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