Geotextiles are specified by a short set of index tests: wide-width tensile strength and elongation, CBR puncture, trapezoidal tear, permittivity or permeability, apparent opening size and UV resistance. The usual methods are ISO 10319 and ASTM D4595 for tensile, ISO 12236 and ASTM D6241 for CBR puncture, and ISO 11058 and ASTM D4491 for water flow. A buyer should write the required values and the method into the purchase order, and have sealed samples tested against them.
The tests fall into two groups. Mechanical tests say whether the fabric will survive installation and carry load, and hydraulic tests say whether it will pass water and hold soil for the life of the structure.
Mechanical tests
- Wide-width tensile (ISO 10319, ASTM D4595): a 200 mm wide strip is pulled to failure and the result is reported in kilonewtons per metre in both machine and cross directions, with elongation at break. The width matters because narrow strips neck and understate non-woven strength.
- CBR puncture (ISO 12236, ASTM D6241): a 50 mm plunger is pushed through a clamped circle of fabric and the peak force is recorded in newtons or kilonewtons. It simulates a stone pressing through the fabric under fill.
- Trapezoidal tear: a cut is made in a trapezoid-shaped specimen and the force needed to continue the tear is recorded. It indicates how a small installation damage will propagate.
- Grab tensile: a narrower test common in North American specifications, reported in newtons or kilonewtons per clamp rather than per metre. It is not interchangeable with wide-width results.
- Cone drop: a cone is dropped onto the fabric from a set height and the hole diameter is measured, used in some European specifications as a dynamic puncture test.
Hydraulic tests
Permittivity, measured under ISO 11058 or ASTM D4491, is the rate of water flow through the fabric per unit of head, reported per second, and permeability is the related coefficient in metres per second. A non-woven filter fabric is expected to pass water much faster than the soil it protects. Apparent opening size, reported as O90 or AOS, is the particle size the fabric will retain, and it is matched to the grading of the soil behind it. Too open and fines wash through; too tight and the fabric clogs.
Durability and conformance
UV resistance is reported as the percentage of tensile strength retained after a set number of hours of accelerated weathering, often 500 hours. Fabric that will sit exposed for weeks on site needs a good value, while buried fabric needs less. Some projects also require oxidation resistance for polypropylene or hydrolysis resistance for polyester, along with a conformance certificate from the plant's own lab.
Plant certificates are a starting point, not proof. Data sheet values are usually minimum average roll values, and a buyer should check whether the plant's lab actually runs the ISO or ASTM method it quotes. An independent test of sealed samples, with the sampling plan recorded, is the only result both sides will accept if there is a dispute.
How we help
We draw sealed samples at the plant and send them to an NABL-accredited lab for the tests in your specification, so the numbers are independent of the plant's own certificate. We also audit the plant, inspect before shipment, supervise loading and send a weekly update, with one approved supplier and one backup. A free 20-minute sourcing review is a quick way to check that your specification is testable before you order.