Geosynthetics is an umbrella term that covers a wide range of synthetic fabrics for ground engineering.

Because many of these materials have overlapping functions and similar names, the topic can seem intimidating and complex on first glance.

To simplify things, we’ve put together a quick guide to help you get to grips with the main product categories: highlighting use cases and key considerations when specifying for your next civil engineering or landscape project, as well as some forward thinking-trends and potential concerns.

Types of geosynthetics:

Geotextiles 

Geotextiles are permeable synthetic fabrics usually made from polymers like polypropylene and polyester. It’s less common but they sometimes come in biodegradable materials like jute and coir.

They come woven, nonwoven, or knitted, and each type provide advantages across separation, filtration and drainage, reinforcement and protection. 

• Woven geotextiles: consist of interlaced yarns in a grid pattern, creating a fabric with high tensile strength, and are primarily used for reinforcement of weak soil and separation of subgrade.

• Non woven geotextiles: are made from needle punched or thermally bonded fibre mesh for a felt-like, porous fabric. Used for filtration and drainage, they trap fines and aggregates while allowing water to pass through due to their high permeability. 

• Knitted geotextiles: provide moderate strength and good flexibility. They are less common and used when moderate reinforcement and drainage are both needed.

Read more about Geotextiles in our recent article here!

Geomembranes

Geomembranes are thin, flexible polymer sheets made from HDPE, LLDPE, PVC or EPDM. They are used as impermeable liners, for containing liquids and gases in environmental or civil engineering works. 

Their uses include:

• Lining reservoirs, lakes, ponds, drainage tanks and irrigation tanks.

• Containing leachate and gas in landfills and waste water retention ponds and basins.

Geomembranes are often combined with other geosynthetics in composite liner systems, to improve protection, drainage and sealing performance. 

When specifying a geomembrane the material is important as different polymers have different properties and applications:

• HDPE – stiff and chemical resistant, making it ideal for landfills and containment works.

• LLDPE – more flexible than HDPE, for easy installation on uneven ground, used for ponds and attenuation systems. 

• EPDM – highly flexible synthetic rubber with strong UV, weathering and temperature resistance, often used for water features and exposed areas where long term flexibility is needed.

Other properties to consider:

• Thickness and density influence mechanical strength, puncture resistance and durability.

• Chemical and UV performance for long term use.

• Permeability and seam quality – seams must be welded or bonded to prevent water ingress.

Geogrids

Geogrids are polymer grid-like materials with large open apertures, designed to provide tensile reinforcement to soils and aggregate.

Usually made from polypropylene, polyethylene and polyester. Their open aperture structure interlocks with and holds surrounding sand, gravel or dirt in place, improving shear strength, preventing deformation and distributing loads over the area of the grid. 

Geogrids are similar to geotextiles and geocells but designed for reinforcement through tensile strength rather than filtration and soil confinement. They are often used in road and railway bases, soft ground, soft ground stabilisation, reinforcing retaining walls and slopes. 

Geogrid variations:

• Uniaxial geogrids are strong in one direction, for retaining walls and slopes.

• Biaxial geogrids are strong in two directions, often used for subgrade stabilisation in pavements and roads.

Woven vs knitted:

• Woven: high strength polymer yarns woven into a flat grid (usually PVC coated) provide high tensile reinforcement for walls and slopes. Woven geogrids have lower aperture sizes and with limited interlock compared to knitted variants.

• Knitted: polymer strips are warp knitted into flexible open mesh structure, offering high pullout resistance and the ability to conform to curved surfaces. For vegetated slopes, green roofs and MSE walls where root growth is expected.

Geonets

Geonets are made from intersecting polymer ribs, creating a criss-cross, net structure, to transfer fluids like water or leachate.

Similar in appearance to geogrids but designed for drainage. Rib geometry creates continuous open channels under load, for a high in-plane flow, making them highly effective drainage media under and behind liners and structures. 

Geonets are used in:

• Landill liner and cap systems

• Behind retaining walls and pavements

• Combined with geotextiles to create drainage geocomposites

Biplanar vs Triplanar:

• Biplanar geonets have two sets of angled ribs to create channels for fluid flow in both horizontal directions. This is useful in flat drainage applications where uniform radial flow matters more than compressive strength.

• Triplanar geonets contain a third vertical rib, roughly doubling compressive strength and in-plane flow under heavy loads. Must be oriented downhill to avoid ponding and hydrostatic build up.

Geosynthetic clay liners

Geosynthetic clay liners (GCLs) are barrier membranes made from a thin layer of bentonite clay between geotextiles and/or geomembranes forming a very low permeability liner or impermeable liner.

Sodium bentonite swells and expands in water, creating a dense, self-healing liner that can repair punctures and seams with migrating clay.

Used to replace compacted clay, easily installed and simply rolled out, reducing labour costs and logistical issues.

GCLs are a greener alternative to geomembranes – their self healing nature means they don’t need to be replaced or repaired when damaged.

Common uses:

• Environmental containment systems

• Landfill liners and caps

• Wastewater or industrial ponds

• Mining heaps

• Reservoirs. 

Geocells

Geocells are 3 dimensional grids with a honey comb like structure, often made from HDPE.

Their cellular structure holds infill like gravel, soil, sand or concrete.

When filled, lateral movement is limited, creating a stiff mattress for even load distributions. This confinement increases foundation strength, stiffness and stability while reducing lateral spreading, rutting and settlement.  

Sometimes the cells are perforated, creating a permeable structure that allows water to drain and prevents ponding within the grid.

Common uses:

• Stabilisation in paved and unpaved roads

• Railway tracks

• Subgrade improvement

• Erosion control

• Retaining structures and slope protection

Geofoam

Geofoam is a lightweight foam fill material, usually expanded polystyrene (EPS) or extruded polystyrene (XPS).

Due to its low density and predictable engineering properties, it is used to reduce loads on foundations, soft soils and retaining structures, while maintaining strength and stability, with minimal long-term settlement compared to soil fills.

EPS blocks are typically 1-2% the density of soil but provide sufficient compressive strength to support embankments, pavements and structures. The lightweight nature of geofoam enables quick installation and reduced labour during construction.

Typical uses include road and bridge approach fills, slope stabilisation, retaining wall back fill, void filling and insulation beneath roads and foundations. Geomfoam has low water absorption so drainage considerations are important in saturated conditions.

Geocomposites

Geocomposites combine two or more geosynthetics to perform multiple functions simultaneously, for instance drainage & reinforcement or filtration & protection.

Combining products can enhance efficiency over individual components.

Geocomposites typically have a structural carrier layer and one or more facing layers for filtration, drainage, protection or reinforcement.

Common geocomposite types include:

• Drainage geocomposites: composed of a geonet bonded to one or two geotextiles. Used for landfill leachate collection, retaining wall and foundation drainage.

• Reinforcement geocomposites: geogrid combined with a geotextile. For soil stabilisation and load distribution in road bases, embankments and reinforced slopes, while also providing separation or filtration.

• Leak detection geocomposites: consist of a geonet and geotextile, placed between geomembrane liners. For leak detection and drainage in landfills, ponds, and reservoirs.

• Protection geocomposites: made from thick nonwoven geotextiles, sometimes combined with a geonet. Used to protect geomembranes from puncture in landfill liners, reservoirs and caps while allowing gas or water drainage.

Look out for these trends in Geosynthetics

• Recycled geosynthetics: the use of post-consumer recycled plastics has increased in recent years. Recycled polymers reduce the need for new polymers and lowers the carbon footprint of creating geosynthetics by up to 70%. Recycled geosynthetics divert waste from landfills while maintaining performance. It is estimated that 20-30% of new geotextile projects will contain recycled content in 2026.

• Bio-based geosynthetics: incorporate natural fibres like jute, coir or sisal (a fibre made from agave plants) into geotextiles and erosion control mats. These materials provide low carbon alternatives and are designed to degrade naturally over their life cycle. Bio-based materials are ideal for temporary applications and vegetation establishment. Hybrids combine polymers and natural fibres for durability and reduced plastic pollution. These are often specified in environmentally sensitive schemes.

• Smart geosynthetics: incorporate optical fibres, strain gauges and conductive threads to monitor stresses in real time. Smart systems detect changes in PH, liquid presence and deformation, alerting operators to potential failures in real time. Smart geosynthetics have become popular in critical infrastructure applications and climate resilient designs.

• New standards and regulations:
  • UK Green Public Procurement policies require lifecycle carbon data for geosynthetics in public landscapes, encouraging sustainable outcomes.
  • Under new EU Green Deal landscape projects must submit EPDs showing 20-40% lower embodied carbon vs traditional materials to qualify for funding.
  • The EU Circular Economy Plan mandates 25-50% recycled content in geosynthetics for public tenders by 2030 and bans landfill disposal of offcuts, while prioritising biodegradable options.

Limitations and risk factors for geosynthetics

• Microplastics: Polymer geosynthetics can shed microplastics and chemicals over their lifecycle, contaminating groundwater and food chains, this leads to long term environmental harm as well as risks to human health.

• Long term durability issues:
  • UV damage: Exposed geomembranes or geotextiles become brittle from exposure to sunlight, reducing their service life.
  • Biological damage: Roots and plant life can puncture liners, while microbes slowly biodegrade chemicals used to seal junctures.

• End of life and disposal: Most polymer geosynthetics are hard to recycle once contaminated with soil or bonded into composite systems. Landfilling or incineration pose environmental risks.

• Greenwashing concerns: Products marked as eco-friendly or sustainable often still rely heavily on synthetic polymers.

Glossary

A few key words and acronyms:

Materials

• HDPE (high density polyethylene) – rigid and durable thermoplastic polymer with high chemical resistance.

• LLDPE (linear low density polyethylene) – flexible polyethylene polymer with good puncture resistance, used to conform to even ground.

• PVC (polyvinyl chloride) – versatile thermoplastic polymer that can be rigid or flexible.

• EPDM (ethylene propylene diene monomer rubber) – synthetic rubber with high flexibility, weathering and UV resistance.

• EPS (expanded polystyrene) – lightweight foam made from expanded polystyrene beads.

• XPS (extruded polystyrene) – closed-cell foam with higher strength and lower water absorption than EPS.

• Polymer – a material made from long chains of repeating molecules, used to make most rubbers, plastics and geosynthetics.

• Post consumer recycled plastics – plastics from used products, recycled to make new materials.

Construction terms

• Tensile strength – maximum force a material can resist when being pulled or stretched before breaking.

• Shear strength – ability of a material to resist sliding when under load.

• Pullout resistance – how well a geosynthetic stays in place when pulled, controlled by friction and interlock.

• Settlement – the movement of ground or a structure over time due to compression.

• Subgrade – prepared soil layer forming lowest structural layer of a foundation system.

• Leachate – contaminated liquid created when water passes through waste or polluted soil.

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And read more about geosynthetics here:

https://www.tensar.co.uk/resources/guides/introduction-to-geosynthetics