If a rock bag spends its life underwater, the question that decides how long it lasts is how the polymer holds up against water itself.
What hydrolysis is
Hydrolysis is chemical degradation in which water reacts with the polymer chain and breaks it. For polyester, the ester linkages in the chain are the point of attack.
As chains shorten, mechanical properties fall. The material loses strength and becomes more brittle, and beyond a point it no longer performs.
Rate depends on temperature, on pH, and on time. Elevated temperature accelerates it substantially, which is what makes accelerated testing possible: expose the material to a controlled elevated-temperature aqueous environment and measure what happens to its properties.
Two conditions worth flagging because they are site-specific:
Alkaline environments accelerate hydrolysis of polyester. Where a site has genuinely high pH — certain industrial discharges, some cementitious environments — that is a question worth raising rather than assuming.
Warm water is more aggressive than cold. A tropical installation is in a different condition from a temperate one.
What EN 12447 does
EN 12447 is the European screening method for hydrolysis resistance of geosynthetics. Broadly, it exposes specimens to water under controlled elevated-temperature conditions for a defined period and measures retained strength afterwards, comparing tested specimens against unexposed controls.
The output is a screening result: how much of its strength the material keeps after that exposure. It is one input to a durability assessment, and its purpose is to establish that the polymer is suitable for prolonged wet service.
What it supports here
EN 12447 is the method behind the in-water service life position:
Approximately 100 years, for units in submerged service, out of direct UV exposure.
Both halves matter. “Submerged” is the environment the hydrolysis testing addresses. “Out of direct UV exposure” is there because underwater the unit is not being weathered, and weathering is a separate mechanism governed by a different method — EN 12224.
This figure is one of only two numbers on the site’s materials pages. It was confirmed directly by the client during the August 2026 accuracy review, and it is always rendered with its condition attached because the condition is part of the claim. See service life in water vs on land.
What the method does not tell you
Worth being clear, because durability testing is frequently over-read:
It is a screening test, not a prediction of your site. Accelerated exposure at elevated temperature is a proxy for long real-time exposure. The extrapolation from one to the other involves assumptions, and a laboratory environment is not a river.
It does not cover mechanical wear. Abrasion from bedload, ice, and debris are separate mechanisms that no hydrolysis test addresses. See puncture, abrasion, ice, and debris.
It does not cover unusual chemistry. Strongly alkaline water, industrial discharge, or contaminated sediment are conditions to raise specifically.
It says nothing about the fill or the installation. A unit whose mesh is in perfect condition still fails as protection if the bed beneath it has been winnowed away. See why scour protection fails.
What we publish
The method, the property it governs, and the laboratory. Not the measured retained-strength value.
That is the standing policy across the test programme, set out in which test standards apply and on test data and standards. Reports and certificates of compliance are issued per project on request.
For a submittal, the honest form of the statement is: hydrolysis resistance is evaluated to EN 12447, tested by an independent laboratory, and it underwrites an approximately 100-year service life for submerged installation out of direct UV. Not a retained-strength percentage.
Questions worth asking about your site
- Will the units be permanently submerged, intermittently submerged, or above water? Different mechanisms govern each.
- What is the water chemistry? pH in particular.
- What is the temperature regime?
- Is there industrial discharge or contamination in the reach?
- How long does the asset need to last? If the answer is 30 years, the durability question is easier than if it is 100.
Where to go next
- EN 12224 and weathering for the above-water mechanism
- Service life in water vs on land
- What degrades the mesh fastest
- Which test standards apply
- Test data and standards
- The materials hub for the rest