Copper pipe has been the default choice for gas installations in the UK for decades. It works. Installers know it. Merchants stock it. And yet, across the industry, a quiet shift is underway. Corrugated stainless steel tubing (CSST) is taking market share, job by job, installer by installer, and the reasons are practical rather than fashionable.
This guide compares CSST and copper gas pipe across the factors that actually matter on site: installation time, material cost, safety compliance, long-term reliability, and flexibility of application. It also looks specifically at Flexigas, the UK's premium 316L CSST system, and what sets it apart.
If you are pricing a new build gas installation, retrofitting a commercial site, or simply weighing up whether to switch from copper, read on.
Corrugated stainless steel tubing is a flexible, corrugated gas pipe designed to replace rigid copper or steel in gas distribution systems. It bends by hand, routes through cavities without joints, and connects using mechanical fittings that require no soldering, flame, or specialist tools.
CSST was developed in Japan in the 1980s and has been used widely across North America, Europe, and Asia for decades. In the UK, the modern CSST market is growing rapidly, driven by demands for faster installation and more adaptable routing in complex buildings.
Flexigas is manufactured from 316L stainless steel, a marine-grade alloy chosen for its corrosion resistance and mechanical strength. The corrugated profile gives the pipe its flexibility while maintaining the pressure ratings needed for domestic and commercial gas systems. A flame-retardant yellow polyethylene cover protects the tubing and provides clear identification as a gas pipe.
Any discussion of CSST in the UK has to start with the standards framework.
The current applicable standard for flexible corrugated stainless steel tubing for gas in the UK and Europe is EN 15266. This is the standard that governs design, materials, performance testing, and fittings.
Flexigas holds BSI Kitemark KM 598726 and is certified to EN 15266. It also carries Gas.BE approval, reflecting its acceptance across European markets. These certifications confirm that Flexigas has been independently tested and approved for gas installation in the UK.
When specifying or approving CSST on any project, confirm that the product you are using carries EN 15266 certification and a valid BSI Kitemark. This is non-negotiable from a compliance and liability standpoint.
Copper has been the standard material for gas pipework in UK residential and commercial buildings for generations. It is well understood, widely available, and there is a vast body of installation knowledge around it.
Copper is a soft metal, which makes it easy to cut and bend. It is resistant to most forms of corrosion under normal conditions. In some instances, copper corrosion can occur, for example in environments with certain water chemistry or unusual atmospheric conditions. It is not very common in the UK, but it remains a possibility worth factoring into long-term maintenance planning, particularly in older properties or unusual locations.
Copper is a commodity metal. Its price is tied directly to global markets, and over the past several years, copper prices have risen significantly and remain volatile. The price of copper pipe is no longer as predictable as it once was.
Flexigas is manufactured from 316L stainless steel. The "L" designation indicates a low carbon content, which improves resistance to sensitisation and intergranular corrosion. 316L is the alloy chosen for marine, medical, and food-grade applications where corrosion resistance must be reliable over very long timescales.
For gas piping, 316L stainless steel offers several material advantages:
• Excellent corrosion resistance in atmospheric and below-ground environments
• High tensile strength relative to its wall thickness
• Resistance to stress corrosion cracking under normal operating conditions
• Long service life with no degradation in flow characteristics
The corrugated profile adds mechanical robustness. The pipe resists kinking, handles building movement, and maintains its cross-section under normal handling. The yellow flame-retardant polyethylene cover adds an additional layer of protection and provides clear visual identification.
Flexigas is available in a full range of sizes to suit domestic, commercial, and light industrial gas installations:
• DN15 (equivalent to 15mm copper): standard domestic supply line
• DN22 (equivalent to 22mm copper): medium domestic, light commercial
• DN28 (equivalent to 28mm copper): commercial and larger domestic
• DN32: larger commercial applications
• DN40: high-demand commercial and industrial
• DN50: maximum capacity for large-scale gas distribution
This range means Flexigas can handle any application from a single domestic boiler connection to a large commercial gas distribution system. Copper is also available in equivalent sizes, but the available sizes in CSST from most suppliers tend to stop at 28mm. Flexigas's range up to DN50 is a meaningful differentiator for commercial installers.
This is where the comparison becomes stark. CSST installation is fundamentally different from copper, and those differences translate directly into time and labour cost.
Installing copper gas pipe requires:
• Measuring and cutting each section to length
• Deburring cut ends
• Soldering or pressing fittings at every joint, every bend, every transition
• Adequate clearance for flame work (soldering) or pressing tool operation
• Waiting for solder joints to cool before pressure testing
• A significantly higher number of fittings on any given run
On a typical house, a gas installation in copper might involve 40 to 60 fittings or more. Each fitting is a potential leak point. Each fitting requires labour time to prepare, connect, and test.
In concealed or tight spaces, copper becomes difficult. Bends require bending tools or elbows. Running through joists, around obstacles, and through wall cavities means multiple sections, multiple joints, and multiple opportunities for errors.
Flexigas runs as a continuous length from one point to the next, with no joints along the run. The pipe bends by hand. It routes through cavities, along joists, through walls, and around obstacles without requiring additional fittings mid-run.
Connections are only needed at each appliance or branch point. A typical house installation with Flexigas might use ten to fifteen fittings rather than fifty. Each connection is made without flame, without specialist tools, and without waiting time.
The Flexigas installation process breaks down into seven steps: cut, remove the cover, slide the nut and collets into position, tighten, wrap with yellow silicone tape, attach the FG Bond earthing terminal, and bond. No soldering equipment. No flux. No hot works permit needed.
Flexigas installations typically save around 75% of the time required for equivalent copper or steel installations. For a gas engineer, this is not a marginal difference. It is the difference between a half-day job and a two-day job.
Flexigas offers three fitting types, each designed for specific applications:
The Classic fitting uses a metal-to-metal self-flare connection. The last corrugation of the tubing deforms into the fitting seat as the nut is tightened, forming a gas-tight seal without any additional materials. No sealant, no PTFE, no O-rings. The seal is purely mechanical.
The Seal-Assist fitting incorporates an O-ring for applications where an additional seal is preferred. This is particularly useful in commercial contexts where high-cycle or high-vibration environments are factors.
FG-Link is a partnership product developed with Flowflex, one of the UK's leading brass fitting manufacturers. The result is the largest fitting range on the UK CSST market, with over 150 configurations. This range covers virtually every connection geometry and transition required on a real installation, from straight connectors to complex multi-way configurations and every appliance connection type likely to be encountered.
The breadth of the FG-Link range is a practical advantage. Installers are not limited by available fittings. Whatever the connection requirement, there is an FG-Link fitting to handle it.
All gas pipework in the UK must be electrically bonded. This requirement exists to prevent the build-up of static charge and to ensure that in the event of a fault, current has a safe path to earth rather than jumping through an unintended point.
With copper pipe, bonding is straightforward because the pipe itself is a conductor throughout its length. With CSST, the earthing requirement is handled via fittings.
The traditional approach to bonding CSST involves oversized or specialised bonding clamps fitted to each connection point. These clamps can be awkward to fit, add cost, and require additional skill to position correctly, particularly in tight spaces.
Flexigas has developed a better solution: FG Bond.
FG Bond is a patent-pending integrated earthing terminal that connects directly to any Flexigas fitting. It is pre-drilled and designed to accept a standard earthing cable, clamped down with a single screw. FG Bond is included in the BSI Kitemark KM 598726, certified to BS 951:2009 for earthing clamps.
The practical benefits are significant:
• No separate bonding clamp to source or fit
• No risk of the bonding clamp slipping or being incorrectly sized
• Consistent, BSI-approved earthing at every connection
• Faster installation: bonding is built into the fitting process, not added afterwards
FG Bond removes one of the more fiddly aspects of CSST installation and replaces it with a purpose-designed, certified solution. For gas engineers who install CSST regularly, this is a genuine quality-of-life improvement. For those new to CSST, it removes a potential source of uncertainty and error.
A common question from installers encountering CSST for the first time is where it can and cannot be used.
Yes. Flexigas can be installed in underground and below-ground applications, subject to the requirements of BS 6891 and IGEM regulations. The 316L stainless steel and polyethylene cover provide the corrosion resistance needed for buried service. This is confirmed in the Flexigas installation manual and is a meaningful capability for new build connections, external runs, and commercial sites.
For below-ground runs, the installation should follow the specific requirements of the applicable standard, including appropriate depth, protection from mechanical damage where necessary, and correct joint access provision.
For installations passing through unvented voids, solid floors, solid walls, and other enclosed spaces, Flexigas DS is available. DS stands for Double Sleeve: it consists of the standard Flexigas inner layer, corrugated stainless steel with a yellow polyethylene cover, surrounded by a second corrugated outer sleeve with its own polyethylene cover. The outer sleeve creates a meaningful air gap between the pipe and the surrounding structure.
Flexigas DS can be used across 100% of installation scenarios, straight from the coil, without any need to add additional sleeving on site. This is a time-saving product for complex installations in new builds where an unvented void may be encountered at any point in the run.
The cost comparison between CSST and copper is more nuanced than it might appear at first glance.
Copper is a globally traded commodity. Over the past several years, copper prices have increased significantly, driven by demand from electric vehicles, renewable energy infrastructure, and grid expansion globally. This trend is expected to continue. The cost of copper pipe is higher today than it was five years ago, and there is no structural reason for it to fall significantly.
Flexigas is priced competitively with equivalent-bore copper pipe. In many cases, Flexigas is the same price or less than copper on a per-metre basis. The specific comparison will vary by diameter, supplier, and market conditions, but the premium that once existed for CSST has narrowed substantially.
The more important comparison is total installed cost, not material cost per metre.
A copper gas installation for a typical house might require:
• 40 to 60 fittings (each with a labour and material cost)
• Several hours of bending, cutting, and soldering
• Additional time for hot works procedures
A Flexigas installation for the same house might require:
• 10 to 15 fittings
• No hot works
• Significantly less cutting and preparation time
When fittings are eliminated, the cost of those fittings is eliminated too. When installation time is reduced by 75%, labour cost drops proportionally. The total installed cost of a Flexigas system is typically lower than an equivalent copper installation once labour and fittings are included in the calculation.
For commercial installations where the scale of labour savings is larger, the cost advantage of Flexigas over copper is even more pronounced.
Both copper and CSST are safe when installed correctly. The relevant comparison points are:
Fewer joints means fewer potential leak points. A Flexigas installation with ten fittings has ten potential leak points. The equivalent copper installation with fifty fittings has fifty. In terms of long-term gas tightness, the CSST approach is structurally more conservative.
Copper soldering requires flame. Flexigas does not. The absence of hot works means no ignition risk during installation, no need for fire blankets or permits, and no waiting for joints to cool before testing. This is a safety benefit on site and a simplification of the installation process.
The FG Bond system provides a consistent, BSI-approved earthing solution at every fitting. There is no ambiguity about whether bonding is adequate because the certified terminal is built into the fitting process.
Flexigas's EN 15266 certification and BSI Kitemark provide independent assurance that the product meets the required performance standards. This is documented, verifiable, and available to inspectors and building control officers.
CSST is not always the right answer. Here is a straightforward guide:
CSST makes most sense when:
• Routing through cavities, joists, or tight spaces where continuous runs save significant fitting cost
• Time on site is constrained and labour cost matters
• The installation involves complex routing with many direction changes
• Commercial volumes justify the investment in a new installation approach
• The installer wants to eliminate hot works entirely
• Long runs are involved where fitting count in copper would be high
Copper remains a reasonable choice when:
• The installation is very simple and short, with minimal routing complexity
• The installer is already fully set up for copper and the job is small
• Local merchant availability for CSST fittings is limited
For most domestic and commercial gas installations in the UK in 2026, Flexigas offers a compelling combination of speed, cost, safety, and compliance. The more complex the installation, the more compelling the case becomes.
The case for CSST versus copper gas pipe in the UK has strengthened considerably in recent years. Rising copper prices have narrowed the material cost gap. The labour savings from CSST installation are well established. EN 15266 certification and BSI Kitemark provide the compliance framework that specifiers and building control need.
Flexigas, manufactured from 316L stainless steel and available from DN15 to DN50, is the most comprehensively specified CSST product on the UK market. The FG Bond integrated earthing terminal is a genuine innovation that simplifies one of the historically fiddly aspects of CSST installation. The FG-Link fitting range, developed in partnership with Flowflex, covers over 150 configurations and handles virtually every connection requirement a gas engineer is likely to encounter.
For gas engineers, contractors, and M&E specifiers evaluating CSST vs copper gas pipe in the UK, Flexigas offers a product that is faster to install, competitively priced, fully certified, and designed to make the job easier at every stage.
*Flexigas CSST is available through UK merchant stockists. For technical specifications, installation guides, and stocking information, visit [flexigas.com](https://flexigas.com).*