A rock bag is two things: a mesh and the stone inside it. The stone provides the mass. The mesh has to keep the stone together for decades, in water, under load, against abrasion, and it is the part that decides the service life.
The polymer: polyester
Polyester was chosen for one property above the others: resistance to hydrolysis, which is breakdown from prolonged contact with water.
That matters because the primary duty is submerged or intermittently submerged. A polymer that degrades in water is disqualified whatever else it does well.
The method that governs the claim is EN 12447, and it is what underwrites the in-water service life position. See EN 12447 and hydrolysis.
Polyester also has good tensile strength for its weight, low creep relative to some alternatives, and reasonable abrasion resistance. It is not the best polymer at everything, and its weaknesses are worth naming: it is more susceptible to strongly alkaline environments than some alternatives, and like all synthetics it is degraded by ultraviolet light when exposed.
Virgin, not recycled
The mesh uses virgin polyester rather than recycled polymer, and the reason is not a microplastics standard, because no published ISO or EN standard measures shedding from a geosynthetic in service. It rests on the properties that are testable: hydrolysis, weathering, oxidation, and consistent specifiable strength.
The position we can support is directional: virgin polymer emits fewer microplastics than recycled polymer in that test. We do not publish a figure for how much fewer, because we have not published measured values and a plausible-looking number here would be invented.
That is a weaker claim than “reduces microplastics by X percent” and it is the one the evidence supports. Virgin vs recycled polymer covers the trade in full, including the environmental argument that cuts the other way.
The weave: raschel
A raschel weave is a warp-knitted structure in which yarns interloop rather than simply crossing over and under.
The consequence that matters is tear propagation. In a woven fabric, a cut strand can start a run: the break travels along the weave and the opening enlarges. An interlooped knit resists that, so damage tends to stay local to where it occurred.
For a product that will be dragged over rock, struck by debris, and abraded by bedload for decades, “damage stays local” is the property that decides whether a puncture is an inconvenience or a failure. The method is tongue tear strength, under ASTM and ISO procedures. See raschel weave explained.
The fill, and the division of labour
Worth stating because it explains the whole product.
In riprap, the individual stone resists the flow, so it must be heavy enough on its own and the gradation is specified accordingly.
In a rock bag, the unit resists the flow. The mesh contains the fill and the assembly behaves as one mass. That has two consequences:
- The fill does not have to be an armor gradation. It has to be larger than the mesh aperture and durable in the environment. See when local stone changes the economics
- The mesh is a structural component, not a container. It carries load during lifting and placement and it holds the mass together in service
That second point is why the tensile and puncture methods matter as much as the durability ones.
What we publish, and what we do not
Plainly, because it is unusual and people ask:
We publish which test method backs which claim, and which laboratory ran it. The programme covers wide-width tensile, static puncture (CBR), and tongue tear under ASTM and ISO; hydrolysis under EN 12447; weathering under EN 12224; and oxidation under BS EN ISO 13438. There is no microplastics method in the programme, because no published standard measures in-service shedding from a geosynthetic. The laboratories are TRI Environmental, SGS, and GTS. It is all set out on test data and standards.
We do not publish measured values. No tensile figure, no puncture figure, no tear figure.
The reason is specific rather than evasive: this is a product a DOT reviewer may rely on, and a plausible-looking number on a web page gets pulled into a submittal and then into a design. Reports and certificates of compliance are issued per project on request, from the laboratory, with the conditions attached.
If your specification requires a minimum tensile value in stated units, we cannot meet it from published material today, and that is better established at specification stage than after award. See getting a non-standard product approved.
The one exception is service life, which the client confirmed directly, and both figures are always stated with the condition they depend on: approximately 100 years in submerged service out of direct UV, and approximately 50-100 years on land when covered within one month of installation. Those conditions are part of the claim, not a footnote. See service life in water vs on land.
Where to go next
- Raschel weave explained
- Virgin vs recycled polymer
- Which test standards apply
- What degrades the mesh fastest
- Test data and standards for the full programme
- When not to use rock bags for what the data does not cover