How Elongation, Recovery and Creep Affect Load Stability in Plastic Strapping Materials

Choosing the right strap for your cargo load comes down to more than just picking the widest or thickest option.  

Temperature changes, humidity and handling can all cause a load to compress, shrink or shift during transport. How your strapping responds to those changes determines whether your load stays secure from the warehouse floor to its final destination.  

Three factors that are often overlooked, elongation, recovery and creep can have a significant impact on the stability of your load. 

In this blog we’ll examine how strap elongation, recovery, creep and width affect load stability – so you can better protect your goods from damage and help your operation reduce losses. 

Simply put, elongation is how much a strap stretches under tension. It's usually expressed as a percentage of the strap's original length. 

Stretching might sound like a bad thing, but it's necessary (in the right amounts) for keeping a load secure. A strap with some elongation helps absorb shocks and impacts during transit.

The problem comes with too much elongation. When a strap stretches beyond what's useful, it creates excess slack. A slack strap can't maintain the tension needed to hold a load together, which increases the risk of shifting, damage or complete strap failure. 

Recovery is the flip side of elongation. It describes how well a strap returns to its original tension after it's been stretched. 

A strap with good recovery bounces back and retakes tension after the load shifts or compresses. A strap with poor recovery stays stretched and creates slack. This leads to the same issues as a strap with too much elongation.  

Together, elongation and recovery determine how well your strapping adapts to a moving load. A strap that stretches appropriately and then recovers its tension is more likely to keep your load stable throughout its journey.

Elongation and recovery describe how a strap reacts to a single force (i.e. a load shifts, compresses and bounces back). Creep describes how the strap maintains tension through constant force over a period of time.  

As creep occurs, the strap relaxes and the tension decreases. If the strap material has poor resistance to creep, the load may loosen during transport, even if the strap was properly tensioned at the start.  
 
Creep plays a bigger role in some applications than others. Long shipment times, heavy pallet loads, high temperatures and compressible products all increase the likelihood and impact of creep.  

Strap width is another variable that affects how force is distributed across a load. 

Two materials make up the majority of plastic strapping applications: polypropylene and polyester. They each have their own advantages, and knowing the difference will help you match the right material to the job. 

Polypropylene (PP)  

PP strapping is cost-effective, available in narrower widths and different thicknesses, and works well for lighter, more stable loads.  

This material has higher elongation and lower recovery than polyester, which makes it a good fit for applications where loads aren't under extreme stress. Plus, its flexibility helps the strap adapt to the surface of irregularly shaped packages. 

Polyester (PET)  

PET strapping offers lower elongation, better recovery and better creep properties than PP. This makes it a good choice for heavier loads, unstable loads or products that expand after strapping.  
 
It also performs better across a wider range of temperatures, making it the stronger option for loads facing varying climates in transit. 

For operations focused on sustainability, PET is a popular choice. It's made from recycled materials and can be recycled again after use. 

No single strap is right for every application. Here are the key factors to consider when evaluating your options: 

Load weight  

Heavier loads need stronger straps with lower elongation. A strap that stretches too much under a heavy load won't maintain the tension needed to keep that load stable. When in doubt, plan for the heaviest load the strap will ever need to handle. 

On the other hand, lighter loads present an opportunity for cost savings, as you may be able to secure the load with a low-cost strap option like PP strapping.   

Load material  

Is your load rigid (e.g. steel, machinery, dense wood) or compressible (e.g. paper, foam, textiles)?  

Rigid loads need strong recovery so the strap doesn't go slack as the load settles. Compressible loads need enough elongation to allow for compression, combined with enough recovery to stay taut as the load pushes back. 

Transit conditions  

Longer transit times, more handling touchpoints and greater temperature variation all increase the demands on your strapping. The more a load is moved, the more opportunities there are for tension loss.  

If your load travels long distances or passes through various climates, PET is the safer choice. 

Speaking with an expert to find the right strap for your application is the best way to ensure your load is properly protected and that you’re getting the most value from your strapping investment.  

On top of our high-quality strapping offerings, EAM-Mosca also has experts at the ready to help you make that decision.  

Contact our team for professional help finding the best strap for your needs.