HDPE vs LLDPE Geomembrane
HDPE and LLDPE are the two polyethylene geomembranes on nearly every containment shortlist, and they weld with the same equipment and cost in the same neighborhood. The split is crystallinity: HDPE trades flexibility for chemical resistance and strength, LLDPE trades chemical margin for the strain capacity to follow a settling subgrade. Pick by whether chemistry or deformation governs the design.
How the two options compare
| Factor | HDPE | LLDPE |
|---|---|---|
| Governing spec | GRI-GM13 | GRI-GM17 |
| Density | 0.940 g/cc or higher | 0.939 g/cc or lower |
| Tensile break elongation (60 mil) | 700 percent | 800 percent |
| Multiaxial strain (ASTM D5617) | Not required by GM13 | 30 percent minimum required by GM17 |
| Stress crack resistance | NCTL required, 500 hours per ASTM D5397 | Inherently resistant; no NCTL requirement |
| Flexibility | Stiff sheet; wrinkles managed during placement | Conforms to subgrade and settles with it |
| Chemical resistance | Broadest of the polyethylenes, including many hydrocarbons | Good in most waters and moderate chemistry; less hydrocarbon margin |
| Seaming | Wedge fusion and extrusion welding, GRI-GM19 values | Same equipment and methods, GM19 values for LLDPE |
| Typical applications | Landfill base liners, heap leach floors, chemical and hydrocarbon containment | Landfill caps and closures, settlement-prone floors, ponds over soft ground |
Same polymer family, different crystallinity
HDPE and LLDPE are both polyethylene geomembranes, made on the same extrusion lines, welded with the same wedge and extrusion equipment, and specified through parallel Geosynthetic Institute standards: GRI-GM13 for HDPE and GRI-GM17 for LLDPE. The property tables even rhyme, with thickness, tensile, tear, puncture, carbon black, and oxidative induction time requirements built the same way.
The difference is resin density, which is a proxy for crystallinity. HDPE sits at 0.940 g/cc and above, where tightly packed polymer chains deliver chemical resistance, tensile strength, and stiffness. LLDPE sits at 0.939 g/cc and below, where branched chains pack loosely and the sheet stays soft. Every practical difference between the two materials falls out of that one number, which is why GM17 writes it as a ceiling and GM13 writes it as a floor.
Chemical resistance: HDPE keeps the margin
HDPE has the broadest chemical resistance envelope of the common geomembranes. It handles low and high pH, brines, landfill leachate, mining process solutions, and many hydrocarbons, which is why it is the default sheet for landfill base liners, heap leach pads, and chemical secondary containment. LLDPE performs well in waters, wastewaters, and moderate chemistry, but its lower crystallinity gives solvents and hydrocarbons an easier path into the polymer, so it carries less margin in aggressive service.
For either material, resistance claims belong to specific formulations and specific fluids. A submittal for chemically loaded service should include the manufacturer's compatibility data for the actual containment liquid, and both GM13 and GM17 sheets carry the same stabilizer verification through standard OIT testing per ASTM D3895.
Strain capacity: LLDPE follows the ground
LLDPE's case rests on deformation. GM17 requires 800 percent break elongation and a 30 percent minimum axi-symmetric break strain per ASTM D5617, a multiaxial balloon test GM13 does not require of HDPE at all. When waste settles under a landfill cap, when ore load presses a heap leach liner into subgrade irregularities, or when a pond floor rides on compressible soils, the liner deforms in three dimensions, and LLDPE tolerates far more of it before failing.
HDPE handles uniform, well-compacted subgrade without complaint, but localized differential settlement puts its stiffer sheet under concentrated strain. HDPE also carries a failure mode LLDPE effectively does not: environmental stress cracking, the slow brittle failure of high-crystallinity polyethylene under sustained stress. GM13 screens for it with a 500 hour notched constant tensile load requirement per ASTM D5397; GM17 omits the test because low-density resin does not crack that way. On a design with sustained multiaxial strain, that difference is the whole argument.
Handling, welding, and field behavior
In the field, the two materials run nearly the same playbook. Panels deploy from rolls, long seams are welded with dual-track hot wedge machines, details are extrusion welded, seams are air pressure tested per ASTM D5820 and vacuum tested per ASTM D5641, and destructive samples are pulled in shear and peel per ASTM D6392 against GRI-GM19 values published for each material and thickness. An installer qualified on one is qualified on the other with the appropriate trial welds.
The daily differences favor LLDPE for handling: the softer sheet conforms to corners and details with less fighting, and it develops smaller thermal wrinkles than HDPE on hot days. HDPE repays the stiffness with a harder wearing surface during placement and the deeper installed base, so crews, resins, and replacement rolls are never far away. Textured versions of both materials are published for slope work in their respective standards.
How designs actually split the difference
Most projects do not choose one polyethylene; they assign each where it is strong. A landfill takes HDPE on the base liner, where leachate chemistry governs and the subgrade is engineered, and LLDPE on the final cover, where the cap must ride decades of waste settlement with almost no chemical demand. A heap leach facility may put HDPE under ponds and solution channels and LLDPE on pad floors where high ore loads meet imperfect subgrade.
When one sheet must do everything, the tiebreakers are the fluid and the ground. Aggressive chemistry or hydrocarbons point to HDPE. Soft ground, settlement, or seismic deformation point to LLDPE. Same thickness menus, same welders, same QA program either way, so the decision can be made on the engineering rather than the logistics.
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