PET, PP and HDPE are polymer names, not interchangeable engineering products. Compare PET and PP geotextiles by their measured filtration, separation, protection or reinforcement properties; evaluate an HDPE geomembrane separately as a barrier. A porous fabric and a continuous sheet perform different functions even when both belong to a composite lining system.
PET reinforcement can have lower creep than comparable PP or polyethylene reinforcement, but this does not make every PET fabric stronger, more durable or more suitable than every PP product. Construction, formulation, temperature, chemistry, loading and installation all matter. Select the function first, then compare traceable product evidence.
First distinguish polymer from product form
| Product being compared | Possible function | Primary evidence |
|---|---|---|
| PET or PP nonwoven geotextile | Filtration, separation or cushioning when appropriately specified | Opening size, flow, installation survivability and grade-specific properties |
| PET or PP reinforcement geotextile | Carry specified tensile loads within reinforced soil | Tensile response, product-specific long-term strength, durability and soil interaction |
| HDPE geomembrane | Restrict liquid migration in a designed containment system | Sheet specification, chemical compatibility, seams and installed integrity |
| Geocomposite | Combine identified functions, such as filtration and drainage | Each component plus assembly performance under the relevant pressure and gradient |
Do not infer properties from polymer density or mass per unit area alone. A geotextile is normally designed to allow water passage; it is not an impermeable liner. Likewise, a geomembrane does not provide soil filtration simply because it is made of a polymer used elsewhere in geosynthetics.
Tensile strength, stiffness and creep resistance
Compare the same test and strain level
ASTM D4595 describes wide-width geotextile tensile testing, including force–elongation behavior and modulus calculations. Compare results obtained with the specified method, direction, conditioning and reporting basis. Grab tensile force, wide-width force per width and resin stress are different quantities.
For a geotextile, tensile force per width T is commonly reported in kN/m. Secant tensile stiffness is J = T/ε, where strain ε is a dimensionless decimal. If T = 15 kN/m at 2% strain, J = 15/0.02 = 750 kN/m. It is not 750 MPa. A resin or fiber modulus in MPa cannot be directly substituted for the measured tensile stiffness of a finished fabric.
Fiber alignment, bonding and fabric construction affect the early part of the load–strain curve. Needle-punched material may show substantial extension before high tensile force develops, but its initial stiffness should not be declared zero without measurement. The relevant strain limit and function determine which part of the curve is useful.
Use product-specific long-term data
The FHWA review of reinforcement reduction factors identifies stress, polymer, manufacturing method and temperature as influences on creep. It reports that PP and polyethylene generally show more creep than polyester under otherwise comparable conditions. This is a trend, not a universal 100-year retention percentage or a prediction for an unidentified fabric.
For reinforcement, obtain the product’s applicable creep/creep-rupture data, design temperature and extrapolation basis. For filtration or cushioning, tensile creep may not be the governing selection criterion: investigate hydraulic performance, compression or puncture protection as appropriate. Do not transfer a result from an HDPE geomembrane, geogrid or resin specimen directly to a geotextile.
Long-term design strength: retain the calculation, qualify the inputs
A common reduction-factor approach expresses reduced tensile strength as Tred = Tult / (RFCR × RFID × RFD), accounting for creep, installation damage and durability. The governing design method determines the strength basis, additional factors, load combinations and system checks. Do not combine factors from unrelated design frameworks.
The following preserves the arithmetic as a hypothetical sensitivity example. The inputs are not verified PET, PP or HDPE product values and are not recommended design factors. Assume the same 200 kN/m short-term strength solely to show the effect of changing the factors.
| Illustrative case | RF for creep | RF for installation | RF for durability | Calculated reduced strength |
|---|---|---|---|---|
| A | 1.5 | 1.1 | 1.1 | 110.2 kN/m |
| B | 2.6 | 1.2 | 1.1 | 58.3 kN/m |
| C | 4.5 | 1.2 | 1.1 | 33.7 kN/m |
For example, 200/(1.5 × 1.1 × 1.1) = 110.19 kN/m, rounded to 110.2. The difference between Cases A and C follows from the assumed inputs; it does not prove that PET is 3.2 times better than PP or that a wall needs three times as many reinforcement layers. Wall geometry, loads, connections, pullout and deformation also need assessment.
Chemical resistance and temperature
PET hydrolysis and polyolefin oxidation are relevant durability mechanisms, but their rates depend on the particular material and exposure. Avoid “immune to acids and bases,” “no biological degradation” or a fixed strength-loss percentage attached to one pH value without a matching test report.
The historical FHWA NHI-10-024 reinforced-soil manual illustrates that PET durability assessment considers pH, molecular weight and carboxyl end groups; its tabulated assumptions include defined molecular-property and environmental limits. It is not a blanket approval of all PET below pH 10. Use the applicable current project requirements and product-specific evidence, particularly for alkaline fill, lime/cement-treated soil or unusual water chemistry.
A melting point is not a maximum operating or installation temperature. Hot asphalt exposure, cold handling and elevated buried temperatures require suitable products and installation instructions. A material remaining below its melting point does not guarantee unchanged tensile properties.
For an HDPE barrier exposed to waste liquids, EPA Method 9090A provides a chemical-compatibility investigation procedure. Its existence does not prove that all HDPE retains more than 95% strength in toluene, hexane or every mixed leachate. Identify the exact formulation, chemical composition, concentration, temperature, duration and acceptance criteria.
Filtration and drainage: use the right units
ASTM D4491/D4491M addresses geotextile water permeability through permittivity testing. Permittivity ψ has units of s−1; hydraulic conductivity k has units of length/time, such as m/s. In-plane transmissivity is a separate property with units of m²/s. They must not share one mislabeled table column.
Under the applicable test assumptions, k = ψt, where t is thickness in consistent units. For an example with ψ = 1.0 s−1 and t = 2 mm = 0.002 m, k = 0.002 m/s = 0.2 cm/s. This is a calculation from assumed inputs, not a performance declaration for every 200 or 300 g/m² fabric. Test head, pressure, direction and conditioning affect comparisons.
Opening size must be matched to the protected soil and test method. Do not label an intact geomembrane “O90 <0.001 mm” to imply absolute impermeability: a geotextile opening-size measure is not the appropriate description of its barrier performance. PET and PP fabric selection needs retention and clogging assessment, not a universal polymer-based flow ranking.
ASTM D5101-23 investigates specific soil–geotextile combinations under the method’s applicable conditions. It cannot establish that every fabric loses exactly 50% of permeability in 24 hours or remains stable for 50 years. Match the laboratory/design assessment to the actual soil and flow environment.
HDPE sheet properties are not fabric properties
GRI-GM13 Revision 19 specifies HDPE sheet properties by type and thickness. Its 500-hour stress-crack test requirement, carbon black range of 2.0–3.0% and specified OIT criteria are test/specification values. They do not prove zero cracking, universal solvent resistance, or 100 years of service. Standard OIT and high-pressure OIT are different procedures and results.
Specify a barrier using the correct sheet and seam evidence, then evaluate defects, penetrations and installation. A puncture result under one method cannot be substituted for a result under another probe geometry. Likewise, water-vapor transmission, diffusion of dissolved chemicals and leakage through an installed seam are different mechanisms.
Composite systems and movement
A geotextile may protect a geomembrane or filter drainage flow, but the layer sequence must follow the approved design. More layers can introduce additional interfaces. Determine protection using the actual aggregate, load and installation conditions, and evaluate interface shear using the actual materials. A quoted friction-angle range is not proof that every 3H:1V slope is stable.
For regulated composite liners, confirm the required membrane-to-mineral contact and drainage arrangement. A generic PET/PP/HDPE stack is not automatically compliant. The GSI document directory separates material specifications, protection assessment and other design guidance because those functions require distinct checks.
Thermal movement is a length calculation: ΔL = αLΔT. If α is assumed to be 2 × 10−4/°C, L = 100 m and ΔT = 20°C, free movement is 0.4 m, not 40 m. A 10,000 m² area cannot be inserted as L. Actual liner movement also depends on restraint, temperature distribution, geometry and contact; the example is not an anchorage or wrinkle allowance.
A practical selection checklist
- State the required function: filtration, separation, reinforcement, protection, drainage or containment.
- Identify the product form and exact grade before comparing polymer families.
- Compare test methods, directions, units, statistical reporting and relevant service conditions.
- Check chemistry, temperature, load, installation damage and long-term behavior for that application.
- Verify interfaces and complete-system performance, including seams where a barrier is involved.
- Request traceable documentation and apply the project designer’s acceptance requirements.
See Jinseed’s nonwoven geotextile and HDPE liner information for the respective product families. Send the required function and specification to request grade-specific data. The examples above are calculations and source-based explanations, not reports of unpublished field trials.
Sources
- FHWA: Synthesis of GRS Design Topics, Chapter 7 (2015) — reduction-factor approaches, creep and limitations.
- FHWA NHI-10-024 (2009/2010), Volume I — historical reinforcement durability guidance; check current project requirements.
- ASTM D4595, ASTM D4491/D4491M and ASTM D5101 — public descriptions of the relevant test scopes.
- GSI: GRI-GM13 Revision 19 (2025) — HDPE sheet specification.
- US EPA: Method 9090A — chemical compatibility investigation.
