Armaflex Installation Guide — How to Fit Armaflex Pipe Insulation

June 7, 2026

Armaflex is one of the easiest pipe insulation products to install, but a poor installation — with unsealed joints, gaps or incorrectly sized insulation — will compromise its thermal and condensation control performance. This guide explains how to install Armaflex pipe insulation correctly, from measuring and cutting through to sealing and finishing.

What You Need

Armaflex pipe insulation in the correct bore size and wall thickness
Armaflex 520 contact adhesive (or Armaflex tape for joints in awkward locations)
A sharp knife or scissors
A steel rule or straight edge
A tape measure
A small brush for applying adhesive
A marker pen

If you are using Armaflex Self Seal, you will not need adhesive for the longitudinal seam, but you will still need it for butt joints between lengths.

Step 1: Choose the Right Size Armaflex

Armaflex is sized by the outside diameter (OD) of the pipe, not the bore of the pipe. The bore of the insulation must match the OD of the pipe you are insulating.

Read our pipe insulation sizing guide and copper pipe size vs insulation size guide for full details.

For wall thickness selection, refer to our Armaflex thickness guide. As a general rule:

13mm wall — domestic hot water pipes in heated spaces
19mm wall — pipes in unheated spaces, Part L compliance, chilled water
25mm wall — refrigeration pipework, high-humidity environments

Step 2: Measure and Cut Straight Lengths

Measure the length of pipe to be insulated
Mark the Armaflex tube with a marker pen at the required length
Cut cleanly and squarely with a sharp knife or scissors — a clean, square cut is essential for a good butt joint
Cut slightly long rather than short — you can trim to fit, but a gap at a butt joint cannot be corrected without a new piece

Tip: A mitre box or straight edge helps achieve square cuts, particularly on larger diameter insulation.

Step 3: Fit Straight Runs

Standard Armaflex (Non-Self-Seal)

Apply Armaflex 520 adhesive to both faces of the longitudinal slit along the full length of the tube
Allow to become touch-dry (2–5 minutes at 20°C)
Open the slit and snap the insulation over the pipe
Press the seam closed firmly along its full length

Armaflex Self Seal

Peel back the release paper from the factory adhesive strip on the longitudinal seam
Open the slit and snap the insulation over the pipe
Press the seam closed firmly along its full length

Step 4: Seal Butt Joints Between Lengths

Butt joints between lengths of insulation must always be sealed with adhesive — even on self-seal tube. An unsealed butt joint is a gap in the vapour barrier.

Ensure both cut ends are clean and square
Apply Armaflex 520 adhesive to both faces of the butt joint
Allow to become touch-dry
Push the two lengths together firmly so the ends are in full contact
Hold firmly for a few seconds

Stagger butt joints where possible — avoid having multiple joints at the same point on adjacent pipes.

Step 5: Insulating Bends and Elbows

Bends are the most challenging part of any Armaflex installation. There are two main methods:

Method 1: Mitre Cutting (Best Finish)

Calculate the number of mitre cuts required for the bend angle (typically 3–5 cuts for a 90° bend)
Mark and cut each mitre at the correct angle using a sharp knife and straight edge
Apply adhesive to both faces of each mitre joint
Allow to become touch-dry, then press together firmly
Work around the bend progressively, one mitre at a time

Method 2: Straight Cut with Stretching (Quicker, Less Neat)

On smaller diameter pipes with a generous bend radius, Armaflex can be stretched around a bend without mitre cutting. Apply adhesive to the seam as normal, fit the insulation and allow it to follow the bend naturally. This method is only suitable for gentle bends on small diameter pipe.

Read our Armaflex pipe bend insulation guide for detailed instructions and diagrams.

Step 6: Insulating Valves and Fittings

Valves, flanges, tees and other fittings require Armaflex sheet insulation cut to shape and wrapped around the fitting. The process is:

Measure the fitting and cut Armaflex sheet to the required shape — a paper template helps for complex fittings
Apply Armaflex 520 adhesive to both the sheet and the fitting surface
Allow to become touch-dry
Wrap the sheet around the fitting and press firmly into place
Seal all edges and joints with adhesive or Armaflex tape
Ensure the sheet insulation butts tightly against the pipe insulation on either side with no gaps

Step 7: Finishing and Inspection

Once all insulation is fitted, carry out a final inspection:

Check every longitudinal seam is fully closed and bonded
Check every butt joint is sealed with no gaps
Check all fittings and valves are fully covered with no exposed pipe
Check that insulation is continuous — any gap, however small, is a potential condensation point on cold pipework
For outdoor installations, apply weatherproofing (Tuffcoat, UV coating or jacketing) over the completed insulation

Common Installation Mistakes

Frequently Asked Questions

Do I need to use adhesive on Armaflex Self Seal?
The longitudinal seam on Self Seal has a factory adhesive strip — no additional adhesive is needed for the seam. However, butt joints between lengths must still be sealed with Armaflex 520 adhesive or tape.

Can Armaflex be fitted on live pipework?
Yes. Armaflex can be fitted on pipework that is in service, provided the pipe surface is dry and within the adhesive's application temperature range (5°C to 40°C). On very hot pipes (above 80°C), allow the pipe to cool before fitting.

How do I insulate a pipe that is already fixed to a wall?
Slit the Armaflex tube along its length (it already has a slit) and snap it over the pipe. You do not need to thread it over the end of the pipe. This is one of the key advantages of Armaflex over rigid insulation.

What is the maximum length I can fit in one piece?
Armaflex tube is typically supplied in 1 metre or 2 metre lengths. Fit as long a piece as practical to minimise the number of butt joints. Fewer joints means fewer potential vapour bridges.

Can I paint over Armaflex?
Yes, Armaflex can be painted with a water-based emulsion paint for aesthetic purposes in exposed locations. Do not use solvent-based paints as these can attack the elastomeric rubber.