Rigid or flexible? What you need to know

What’s best for which installation: plastic or metal? Richard Bateman, product marketing manager at RWC, looks some of the factors, including cost, ease, sustainability and performance.

There’s more to deciding on metal or plastic than you might think. As a general rule, copper is the most commonly used metal in plumbing pipework: the only exception is in some healthcare piping applications, where stainless steel is seen more often.

Both copper and plastic pipes are used across a range of new-build and retrofit applications. Plastic pipes are typically made from polybutylene or cross-linked polyethylene (PEX), which can be used separately or together.

When only metal will do (mostly)

For the most part, there are three situations where using metal is more suitable. The first is for gas applications, where copper is the choice. The second is for direct connection to a boiler.

The third situation where metal has an advantage is where the pipework’s on show and it needs to look a certain way. While you can paint plastic pipes, most people agree that metal definitely has the edge when it comes to aesthetics.

After that, plastic and metal are pretty much interchangeable, even for applications such as the internal water supply.

The ease factor

There’s no doubt that plastic is easier to work with than metal, and that’s important when you’re trying to push through heavy workloads or deal with tricky installations.

Most metal pipes come in rigid straight lengths, which need to be cut to size and fitted to shape. Plastics are often supplied in coils, which means you can run continuous lengths with fewer joints and in confined spaces.

Plastic is particularly good for retrofit, where the pipework challenges are rarely straightforward. Because it can be formed into loops quickly and easily, plastic is also ideal for underfloor heating or when you’re running pipes through joists or in confined spaces.

It’s not just space that’s tight either. With the rising cost of materials and tight budgets, that’s another reason to think plastic.

Cost and performance

Metre for metre, plastic pipes come in at about one-quarter of the cost of metal. And, unlike metal pipes – which require connections at regular intervals – plastic can bend around corners and be manipulated into place without extra fittings, saving you money as well as time. Fewer fittings also means less risk of leaks and less remedial work, which is an important consideration when the majority of pipework is hidden.

Plastic is no more susceptible to rodent attacks than metal.

Rats and mice don’t discriminate: they have phenomenal teeth that can eat through anything in their way, whether it’s bricks, concrete or even metal. The issue here isn’t the pipe, it’s the creature.

Plastic scores highly on durability too. When water freezes, copper pipes don’t expand, which can result in damage to the pipe.

What type of plastic?

Head to head, plastic comes out ahead of metal on many measures, not least because it’s cheaper, more durable, and easier to use. So sometimes the choice isn’t between metal and plastic but about which type of plastic.

There’s a binary choice: polybutylene is a highly flexible ‘bendy’ pipe that lays flat straight from the coil, while PEX also comes in coils and can be bent but is a little more rigid and harder to manipulate. Actually, you could use either for pretty much any application, but in reality they’re more suited to specific situations.

Polybutylene: the flexible choice

Due to their material properties, polybutylene pipes are flexible and easy to manipulate. When you need a bend, you simply create the shape you want, and it will hold in place with pipe clips. This makes installation quick and easy, saving time and effort. It’s best suited for anywhere requiring non-linear pipework, including underfloor and retrofits or, for example, a dishwasher. It can also be used for straight applications, making it ultra-flexible.

However, there are times when a more rigid application is required. This includes a straight run to an appliance or up through a wall. Here, PEX is the better option, especially because it’s available in three colours: white, blue, and red, which means you can clearly identify between cold and hot water supplies.

As with polybutylene, it’s versatile and can also be used in other applications, including underfloor, where their added insulation properties are useful. However, because it’s a little less flexible, it will require cold form bends to hold its shape.

Tips and guidance

Whichever you choose, it’s important to follow the manufacturer’s instructions and install them correctly. Of these instructions, perhaps the most important of all is to make sure you’re using the right-sized pipe insert in solid-floor applications, high-risk areas and whenever you’re working through walls. Getting this right protects the pipe from damage caused by movement or thermal expansion. n www.jgspeedfit.co.uk