How to bend multilayer pipe: springs, benders and minimum radius

The aluminium layer in multilayer composite pipe (MLCP) is what makes it bend and stay bent. Plastic-only pipe springs back. Copper needs a spring or a machine for every bend. MLCP sits in the middle: it bends by hand and holds the shape, which is why one bend can replace an elbow and two joints.

The same aluminium layer is also why bending needs some care. Bend too tight and the pipe flattens or kinks, which restricts flow and weakens the wall. This guide covers the minimum radius, when to use hand, spring or bender, how to bend underfloor heating loops and manifold tails, and what to do if a bend goes wrong.

What is the minimum bend radius for multilayer pipe?

The usual rule for bending by hand is 5 times the pipe's outside diameter. One manufacturer gives these minimum radii for its multilayer pipe, bent without a spring.

Pipe size	Min radius by hand	Pipe used in a 90° bend
16 × 2mm	80mm	About 126mm
18 × 2mm	90mm	About 141mm
20 × 2mm	100mm	About 157mm
26 × 3mm	130mm	About 204mm
32 × 3mm	160mm	About 251mm

The radius is measured to the centre line of the pipe. The last column is the length of pipe that goes round a 90° bend at that radius (radius × 3.14 ÷ 2), which helps when you set out a run. For 25mm pipe, the same 5 × diameter rule gives 125mm.

Some pipes bend tighter. One manufacturer says its multilayer pipe can bend to a radius up to 40% smaller than standard multilayer pipe. A spring or bender also lets you go tighter than by hand. Manufacturers do not publish a single figure for that, so check the data sheet for the pipe you are using.

When should I bend by hand, with a spring or with a bender?

Use your hands for wide curves, a spring for tighter bends in 16 to 20mm pipe, and a bender for tight, repeatable bends and for 25 and 32mm pipe.

Method	Best for	Watch for
By hand	Wide curves, UFH loops	Keep to 5 × OD or more
External spring	Tighter bends, 16 to 32mm	Spring must match pipe size
Lever bender	Neat 90°, larger sizes, repeats	Right former for the size

An external bending spring slides over the pipe and supports the outside wall through the bend. Spring makers describe the same job: tight bends without the risk of kinking or severe flattening in the bend.

The MLCP Manual Pipe Bender has an interchangeable former for each size from 16 to 32mm and bends up to 90°. A bender gives the same radius every time, which matters on exposed pipe where bends sit side by side.

How do I bend MLCP with a bending spring?

Slide the spring over the pipe so its middle sits where you want the bend, then bend slowly and evenly with both hands. The steps are the same for every size.

1. Match the spring. Use the spring marked for the pipe's outside size: 16, 20, 25 or 32mm.
2. Mark the bend. Mark the centre of the bend on the pipe, and slide the spring over until it is centred on the mark.
3. Bend with your thumbs. Hold the pipe either side and press with your thumbs on the inside of the bend. Work the pipe round a little at a time, not in one pull.
4. Check the angle. Hold it against a square or the wall. MLCP holds the shape, so what you see is what you get.
5. Slide the spring off. Pull it along the straight leg. Do not twist it off the bend.
6. Look at the bend. It should be round all the way through, with no flat spot or crease on the outside.

Get the angle right first time where you can, and avoid bending the same spot back and forth.

How do I use a multilayer pipe bender?

Fit the former for the pipe size, set the pipe in the former and roller, and pull the lever smoothly to the angle you want. A former for one size will only bend that size properly.

1. Fit the right former. Match it to the pipe's outside diameter.
2. Mark the pipe. Mark where the bend should start or where its centre should be, and line the mark up with the former.
3. Pull smoothly. One steady movement gives the cleanest bend. A plumbing training guide on bending makes the same point for pipe benders generally.
4. Allow a little spring-back. Bend a touch past the angle if needed, but do not over-bend and then pull it back.
5. Release and check. Check the angle and the shape of the bend before you fix the pipe.

For exposed runs, take the coil set out first. A roller pipe straightener for 16 and 20mm pipe gives a straight leg on each side of the bend, so the run looks like it was made from lengths.

How do I bend underfloor heating pipe at the end of each run?

At the end of each run, the pipe turns 180° to come back. With 16mm pipe, keep that turn at 80mm radius or more, so a straight U-turn only works at 160mm spacing or wider.

• 150 and 200mm centres: a U-turn at 75 or 100mm radius. At 150mm, swing slightly wider at the turn to stay above 80mm.
• 100mm centres: a straight U-turn would need a 50mm radius, which is too tight. Use a keyhole return, where the pipe swings wide then comes back into line, or a spiral layout, where most turns are made at twice the spacing.
• Routed boards and castellated panels: the turns are formed into the board or set by the bosses. Follow the pattern rather than forcing a tighter turn.

Our guide to underfloor heating pipe centres covers spacing and layouts in full. In joisted floors, the pipe has to turn through notches or holes at each end, which is covered in UFH in joisted timber floors.

How do I bend pipe up into a manifold?

Where loops rise from the floor to the manifold, use a support bend to hold a 90° turn at a safe radius. A pipe support bend clips over the pipe and holds the bend so it cannot flatten as the screed or floor goes down.

• Use one for every flow and return tail, which is two per loop.
• Leave a straight length at the top, so the pipe goes square into the Eurocone fitting.
• Keep tails in line and evenly spaced. It makes the manifold easier to connect, label and service.

The same rule applies at every fitting. Leave a straight length so the pipe enters square and fully home. Do not bend right up to a press or compression fitting.

What should I do if multilayer pipe kinks?

Cut the kink out. A kinked or flattened section cannot be trusted once bent back. Straightening it hides the damage rather than repairing it.

• On a short run: replace the length.
• On a loop or a long run: cut out the damaged part and join with a coupling, if the pipe maker allows a joint in that place. Our MLCP multilayer pipe guide covers joining and where joints can go.
• Never heat it. One manufacturer says to keep its multilayer pipe away from naked flames.

Pulling loops off a coil by hand can twist the pipe. A decoiler, or rolling the coil out, avoids that. Store coils covered and out of direct sunlight, as one manufacturer advises.

Frequently asked questions

Can you bend multilayer pipe by hand?

Yes. MLCP bends by hand and holds its shape. Keep the radius at 5 times the outside diameter or more, such as 80mm for 16mm pipe.

What size bending spring do I need?

The same as the pipe's outside size. MaxHeatUFH external springs come in 16, 20, 25 and 32mm.

Can I use a copper pipe bender on MLCP?

Use a bender with formers made for multilayer pipe. A bender former only bends the size it is made for, and the pipe sizes differ: MLCP is 16, 20, 25 and 32mm, copper is 15, 22 and 28mm.

Can I heat multilayer pipe to bend it?

No. Bend it cold with a spring or bender. One manufacturer advises keeping multilayer pipe away from naked flames.

How tight can 16mm UFH pipe bend?

About 80mm radius by hand, which is 5 times its 16mm diameter. That is why a straight U-turn at 100mm pipe centres is too tight and needs a keyhole or spiral layout.

Is a kinked MLCP pipe usable if I straighten it?

No. Cut out the kinked section and replace it, or join it with a suitable fitting where the pipe maker allows a joint.

Does bending instead of using elbows save money?

Yes. Each bend replaces an elbow and two joints. That saves fittings and time, and there are fewer places that could leak.

Sources: Bending pipe (Level 2 plumbing resource), MaxHeatUFH tool product data