Woven and nonwoven geotextiles must be compared by the required function and measured properties—not a blanket rule that woven means strength and nonwoven means drainage. Woven constructions differ substantially, while nonwoven grades vary by polymer, fibre structure and bonding. Compare tensile response, soil retention, hydraulic behavior, installation survivability and durability on the same test basis.
This article explains the technical distinction between strength and filtration. For commercial quotation checks, use the geotextile buying comparison; detailed selection also requires the specified soil and loading conditions.
Start with construction and intended function
Woven fabrics interlace yarns or tapes; slit-film, monofilament and multifilament products can have different mechanical and hydraulic behavior. Nonwoven fabrics bond or mechanically interlock fibres, including needle-punched constructions. Neither category has a single universal strength, flow rate or design life.
| Function | Primary questions | Insufficient evidence |
|---|---|---|
| Separation | Will the layer prevent unacceptable soil–aggregate mixing and survive installation? | Colour, nominal GSM or a retail grade number |
| Filtration | Will the soil–fabric system retain soil while passing the required water without unacceptable clogging? | Clean-water flow alone |
| Reinforcement | What tensile response and long-term design strength are required at the permitted strain? | Grab breaking force alone |
| Geomembrane protection | How does the liner–fabric–aggregate system perform under the actual load? | A fixed fabric weight or breaking elongation |
| In-plane drainage | What flow remains under the specified confinement and boundary conditions? | Cross-plane permittivity relabelled as drainage capacity |
Compare tensile properties using the same method
ASTM D4632/D4632M is a grab breaking-load and elongation index test. ASTM D4595/D4595M measures wide-width tensile properties. A result in lbf or N is not interchangeable with a result in kN/m; dividing a grab load by the grip width does not create a valid wide-width value.
Check machine and cross-machine directions independently. Review the stress–strain response where reinforcement is intended, rather than only the breaking point. Long-term design also considers creep, installation damage, environmental durability, connections and the design method. A 120-year design period cannot be inferred from a generic polyester description.
Minimum average roll values, typical values and individual specimen results have different meanings. Verify which basis the project requires and how sampling and lot acceptance are handled. A typical value above the requirement does not guarantee every delivery is compliant.
Distinguish puncture, tear and system protection
ASTM D6241 uses a 50 mm probe for an index puncture assessment. Its force result is not a permitted truck load or a direct simulation of every sharp aggregate contact. A higher result does not justify dropping large rocks onto unprotected fabric or liner.
Tear propagation and puncture describe different damage mechanisms. Installation method, aggregate shape, cover, support and equipment movement affect survival. Where protecting a geomembrane is the main function, use a suitable protection assessment for the actual system; tensile elongation alone does not demonstrate that a liner will remain intact.
Evaluate retention, water passage and clogging together
ASTM D4751 addresses apparent opening size. AOS is not an absolute cutoff below which no soil particle can pass. Select against soil gradation, hydraulic conditions and applicable design criteria; a stable soil filter system may involve particle rearrangement. “No. 70 for all silt” and “No. 100 for clay” are not valid universal rules.
ASTM D4491/D4491M concerns normal-to-plane water passage expressed as permittivity. Distinguish this from hydraulic conductivity and from in-plane transmissivity. Clean-water results do not include every effect of confinement, soil intrusion, blinding, biological growth or mineral deposition.
Check the flow units before comparing them with rainfall
Using US gallons, 5 gal/min/ft² is approximately 12,224 mm/h of equivalent water depth, whereas 2 inches/h of rainfall is 50.8 mm/h. The clean-water test figure is about 241 times that rainfall intensity, so it cannot correctly be described as inherently lower. Nevertheless, it does not prove field drainage adequacy: contributing catchment area, head, soil flow, clogging and the outlet must all be considered.
For an idealized cross-plane calculation, Q = ψ × Δh × A. With permittivity ψ = 1.5 s⁻¹, head difference Δh = 0.05 m and effective area A = 1 m², Q = 0.075 m³/s, or 75 L/s. This is an illustrative test-condition calculation, not a guarantee that a trench or pipe will discharge that quantity.
Reconcile mass and thickness without treating them as performance ratings
One oz/yd² is approximately 33.91 g/m²: 4, 8 and 16 oz/yd² correspond to approximately 136, 271 and 542 g/m². One mil is 0.0254 mm, so 150 mil is 3.81 mm, not approximately 2 mm. Geotextile thickness also depends on the specified measurement pressure.
These conversions help compare documents but cannot establish puncture protection, filtration or reinforcement. Two products with the same mass can differ in polymer, structure and performance. Compare current grade-specific data rather than filling gaps with assumed values.
Select for the project and preserve installation continuity
- Road base: distinguish separation, stabilization and designed reinforcement; soil strength alone does not determine a universal fabric strength or aggregate thickness.
- Drainage trench: check the soil–filter combination and discharge path. A suitable woven monofilament may be an option; not every woven product is a low-flow tape fabric.
- Retaining structure: distinguish reinforcement layers from drainage filters. Layer spacing, tensile demand and stability require design.
- Riprap or liner protection: assess placement damage and the full contact system; nominal weight does not authorize uncontrolled rock drops.
Use approved overlap or seam details, appropriate handling and controlled cover placement. An overlap preserves coverage but is not automatically a structural tensile connection. Avoid driving or turning on exposed fabric. Do not heat unknown fibres until they smoke as a field joining method.
Check exposure limits and procurement evidence
ASTM D4355/D4355M evaluates geotextile deterioration under specified xenon-arc exposure. A laboratory retention percentage cannot by itself predict an exact number of permissible outdoor days or buried service years. Follow the actual storage and exposure requirements and investigate damaged material before installation.
For a nonwoven geotextile proposal, identify the function, soil, water conditions, load, required tests, acceptance basis and quantity. Request traceable product documents and obtain the project’s approval for any substitution.
