Sekisui Chemical has been manufacturing Fibre Reinforced Foamed Urethane (FFU) synthetic rail sleepers and bearers since 1980. The material is made from a pultrusion process, where continuous glass fibres are soaked and mixed with polyurethane, heated, moulded and cut to length. The product is a high-quality composite material with a long-life expectancy, lighter than a hard wood but with the same workability.
Since originally being installed by the Japanese Railway in 1980, FFU has been widely used on Japan’s railway infrastructure including its high-speed bullet train line, the Shinkansen. It is now also installed on railway tracks in over 35 countries around the world on bridges, plain line, and switches and crossings.
Certified
In 2025, NWR awarded Sekisui full certification for FFU Plain Line sleepers for speeds up to 125mph and approved its use on all track categories up to Category 1A. This is a major milestone in Sekisui’s development of the UK business, giving us the opportunity to offer our client a plain line FFU product that can cover all speeds and categories of track.
This certification is the cumulation of two separate trials completed over a four-year period:
East Coast Main Line Bridge 257 near Grantham – at a line speed of 125mph at Track Category 1A, where the FFU sleepers were installed on both the Up Fast and Down Fast lines.
The Roberts Road Trial site in Doncaster, which offered a tight radius curve of 235m which carried heavy freight at 35mph.
The Roberts Road Trial site had been problematic for years. With both timber and concrete sleepers suffering from indentation and gauge spread, the existing sleepers often had to be replaced in under two years. The trial provided proof that the FFU sleepers were resilient to baseplate indentation and gauge spread with a life expectancy that far exceeds the alternative products.
While both trials were being conducted in the UK, Sekisui was invited by Irish Rail to take part in a major project. ‘The Dublin Loop line’ which passes through the centre of Dublin carries the very busy DART passenger services. For this we worked closely with our excellent partners GPX Rail and Irish Rail to replace life expired track on a tight curve of 265 metres through the centre of Dublin. Irish Rail was already familiar with FFU having used the product previously on Bridge projects and several switch and crossing renewals.
GPX Rail drilled and fitted more than 7,000 Schwihag check curved baseplates within a very short timeline and delivered the finished sleeper to Irish Rail’s Portlaoise depot on time for pre-building into track panels. This project was 18 months in the planning and was installed by Irish Rail over Christmas 2024 without incident and on time.
To offer improved lateral stability to our sleepers, the addition of an Under Sleeper Pad (USP) is an option. Lateral stability testing of our FFU sleepers was completed by Southampton University. With the USP fitted, lateral resistance is equivalent with concrete sleepers thus offering a huge advantage for track bed resilience during hot weather.
Proven
Why do Network Rail and Irish Rail track engineers choose FFU for plain line track?
- FFU has a proven life span of 50 years plus.
- It stands alone in that FFU has been in track continuously since 1980.
- It has higher strength and durability than its rivals handling over 30 tonnes in axle loads.
- It’s light weight (740kgs/m3) and is form retentive.
- It doesn’t take ingress of water and will not rot.
- It is thermally resistant and has been tested in the range -65 to +50 degrees Celsius.
- Proven benefits on tight radius curves, through level crossings and across sensitive structures.
FFU plain line is highly recommended for the following applications:
- Over ballasted bridge decks.
- Track though level crossings.
- Train refuelling roads/carriage wash roads in depots.
- Platform lines with subways and areas with complex structures (brick arch viaducts).
- Areas with tight restrictions where shorted ended or variable length sleepers may be required.
- Plain line track and sidings.
Sustainable
The use of FFU plain line sleepers in the UK and Ireland is not only a step forward in track performance and reliability, but also in sustainability. By eliminating the need for repeated replacements, FFU dramatically reduces material use, waste, and the associated carbon footprint over its 50+ year lifespan.
Unlike timber, it does not require treatment with preservatives, and unlike concrete, it avoids the high energy consumption and emissions linked to production. Its lightweight nature also eases transportation and installation, cutting fuel use and site disruption.
With durability, adaptability, and proven longevity, FFU offers track engineers a solution that supports both operational efficiency and environmental responsibility – a combination that makes it a truly sustainable choice for the future of rail infrastructure.
