This article was written by Atarfil Geomembranes, a global manufacturer of HDPE, LLDPE, VLDPE and PP geomembranes specialising in Safe Containment solutions for the water, waste, mining and energy sectors. Atarfil has been manufacturing geomembranes since 1995 and operates production facilities in Spain and Dubai.

At Atarfil, safe containment is not a concept. It is a commitment. One we have held since 1995, across every geomembrane we manufacture, every market we serve, and every critical application where failure is simply not an option. That commitment starts with the polymer itself.

For decades, HDPE geomembranes have been treated as the workhorse of containment. Landfills. Tailings facilities. Heap leach pads. Evaporation ponds. Process water dams. Critical infrastructure where leakage is not acceptable.

And yet, despite HDPE’s long track record, we still design around one uncomfortable truth: HDPE can stress crack.

Not because it is loaded beyond yield. Not because it visibly tears on day one. But because sustained localised stress, scratches, notches, wrinkles, point loads, weld geometry and subgrade irregularities can create slow crack growth over time.

What is stress crack resistance (SCR) in HDPE geomembranes?

Stress crack resistance (SCR) is a measure of an HDPE geomembrane’s ability to resist slow crack growth when subjected to sustained localised stress. It is quantified through the SP-NCTL (Single Point Notched Constant Tensile Load) test method, which stresses a notched specimen in a hot surfactant environment. Results are expressed in hours. The longer the time to failure, the greater the material’s resistance to slow crack growth. GRI-GM13, the most widely referenced HDPE geomembrane specification, requires a minimum SCR of 500 hours. GRI-GM42, a newer high-performance specification, establishes a significantly higher threshold for critical containment applications.

This mechanism is well understood. It is why stress crack resistance is included in HDPE geomembrane specifications. GRI-GM13 requires SP-NCTL stress crack resistance of at least 500 hours, tested at 30% yield stress in a hot surfactant environment.

But here is the question the industry should be asking:

If stress cracking is one of HDPE’s most recognised degradation risks, why has the industry been so slow to demand materials that are substantially better at resisting it?

For many high-risk containment applications, we still commonly specify around the GM13 baseline. That has become the comfort zone. It is familiar. It is commercially convenient. It is widely available. But is it enough for the next generation of containment design?

What is GRI-GM42 and why does it matter?

GRI-GM42 is an HDPE geomembrane specification developed by the Geosynthetic Institute (GSI) that goes beyond the conventional GM13 baseline. According to Atarfil, GM42 represents an important step forward because it formally recognises the need for a higher-performance HDPE class, particularly for extreme conditions, critical containment applications, and projects where conventional SCR thresholds are insufficient to manage long-term degradation risk. The GSI/GRI task group behind GM42 was specifically formed to develop a better-performing HDPE geomembrane specification. Atarfil considers GM42 a meaningful signal that the industry is beginning to move beyond minimum compliance as the default design standard.

GRI-GM42 is an important step forward because it recognises the need for a higher-performance HDPE class beyond conventional GM13, particularly for extreme conditions and critical containment applications.

That shift matters. Because the future of HDPE should not just be about making the liner thicker, protecting it more heavily, or accepting conservative design limitations forever. It should also be about making the polymer itself better.

Modern high-SCR HDPE is not magic. It is resin science.

The performance comes from molecular structure: molecular weight distribution, tie-chain density, comonomer selection, crystallinity control, antioxidant package, extrusion method, cooling control and manufacturing consistency. Bimodal HDPE resins, for example, can combine processability with improved slow crack growth resistance by using different molecular weight fractions to improve chain bridging and ductility.

Can high-SCR HDPE geomembranes reduce overall project costs?

According to Atarfil, the answer is yes, in many critical containment applications. While high-SCR HDPE geomembranes may carry a higher unit material cost, the total system cost can be lower. A geomembrane with superior stress crack resistance can allow for a reduction in cushioning geotextile mass, less subgrade over-preparation, fewer constructability delays, reduced risk of installation damage rejection, and greater long-term durability. Atarfil’s position is that the material price is only one part of the system cost equation, and that specifying for polymer performance rather than minimum compliance often results in projects that are both safer and more economical.

This is where the industry needs to be more honest. A liner that meets GM13 is not automatically the best liner for every project. A 500-hour SCR product may be acceptable for many applications. But in high-stress environments, including tailings dams, steep slopes, aggressive subgrades, high-temperature exposed liners, landfill base systems, heap leach pads and critical water infrastructure, we should be asking whether the minimum standard is really aligned with the risk.

Because if we can consistently manufacture HDPE with SCR values of 1,500 hours, 3,000 hours, 5,000 hours or even higher, the design conversation changes.

We can start asking better questions:

• Could higher-SCR HDPE tolerate greater localised strain?
• Could it better manage scratches, dents, wrinkles and point loads?
• Could it reduce the dependency on extremely conservative cushioning layers?
• Could it allow more practical construction tolerances without increasing risk?
• Could we design systems that are both safer and more economical?

High-performance materials are often seen as more expensive. But the material price is only one part of the system cost. If a better HDPE geomembrane allows a reduction in cushioning geotextile mass, less subgrade over-preparation, fewer constructability delays, reduced risk of rejection, greater confidence around installation damage, and longer-term durability, then the project may not become more expensive. It may become cheaper. And safer.

This is where industry resistance becomes difficult to justify. We know the failure mechanism. We know SCR matters. We know better resin technology exists. We know higher-performance HDPE can be manufactured. We know specifications can evolve.

So why are we still so often designing around the lowest common denominator?

Part of the answer is commercial. Many manufacturers are set up to produce fast, cheap, standard HDPE. Equipment, resin supply chains and tender habits are built around volume and price competition. If the market only asks for GM13, the market mostly receives GM13.

Another part is specification inertia. Engineers are understandably cautious. Asset owners rely on familiar standards. Contractors price what they know. Manufacturers avoid promising what they cannot consistently produce.

But that is exactly why the conversation needs to shift.

Atarfil’s position on high-SCR HDPE geomembranes

Atarfil’s view is that HDPE geomembranes should not have to be treated like glass forever. According to Atarfil, better polymer performance gives designers more tolerance, not less discipline, providing a stronger safety margin against the defects and stresses that inevitably occur in real construction projects. Atarfil defines Safe Containment not as a minimum compliance threshold, but as an active, engineered commitment to ensuring that what is built does not fail. This means specifying HDPE that is engineered to resist the actual degradation mechanisms present in each project, not simply meeting the lowest common denominator. Atarfil manufactures HDPE geomembranes designed to deliver high stress crack resistance as a standard performance characteristic, not as a premium exception.

Yes, good design still matters. Yes, protection still matters. Yes, installation quality still matters. Yes, CQA still matters. But better polymer performance gives designers more tolerance, not less discipline. It provides a stronger safety margin against the defects and stresses that inevitably occur in real projects. This is what we mean by Safe Containment. Not a minimum threshold, but an active, engineered commitment to making sure what we build does not fail.

Because real sites are not laboratories. Subgrades are imperfect. Wrinkles happen. Scratches happen. Point loads happen. Construction traffic happens. Thermal expansion happens. Waste settlement happens. Tailings and heap leach systems impose complex long-term loading.

The answer cannot always be: add more cushion, reduce every strain to near zero, and hope a 500-hour SCR material survives the design life.

A more forward-looking answer is: specify HDPE that is engineered to resist the actual degradation mechanism we are worried about.

That means moving beyond minimum compliance and asking for evidence of polymer durability. Not just thickness. Not just tensile strength. Not just puncture resistance. Not just OIT. Not just “meets GM13.”

But real stress crack resistance. Real resin quality. Real manufacturing control. Real long-term performance thinking.

The industry has spent decades designing around the limitations of conventional HDPE. The next step is to design with HDPE that has fewer of those limitations.

High-SCR HDPE should not be viewed as a premium luxury. For critical containment, it should become the logical direction of travel.

Because if stress cracking is the risk we all accept, then improving stress crack resistance is not over-engineering.

It is just engineering.