Armaflex Pipe Insulation — The Smart Fix for Frozen Pipes

June 7, 2026

Armaflex Pipe Insulation The Smart DIY Fix For Frozen Pipes

A burst pipe caused by freezing can cause thousands of pounds of water damage in minutes. It is also almost entirely preventable. Armaflex pipe insulation is the most effective way to protect vulnerable pipework from freezing — and it is straightforward enough for a competent DIYer to fit in an afternoon.

This guide explains why pipes freeze, where they are most vulnerable, what thickness of Armaflex you need and how to fit it correctly.

Why Do Pipes Freeze?

Pipes freeze when the water inside them drops to 0°C and begins to turn to ice. As water freezes it expands by around 9%, generating enormous pressure inside the pipe. Copper, plastic and steel pipes can all split under this pressure, causing a burst pipe that floods when the ice thaws.

Freezing is most likely in:

Unheated loft spaces and roof voids
External walls and wall penetrations
Garages, outbuildings and unheated utility rooms
Underfloor voids and crawl spaces
External condensate pipes from condensing boilers
Garden tap supply pipes

The solution is simple: insulate the pipe so it retains enough heat to stay above freezing even when the surrounding air temperature drops well below 0°C.

Why Armaflex is the Best Insulation for Frozen Pipe Prevention

Armaflex is a closed-cell elastomeric rubber foam manufactured by Armacell. It is the professional standard for pipe insulation in the UK for good reason:

Low thermal conductivity — 0.033 W/mK, meaning it slows heat loss from the pipe very effectively
Closed-cell structure — does not absorb moisture, so it maintains its insulating properties even in damp loft spaces
Flexible — bends around corners and fits over fittings without gaps
Long service life — properly installed Armaflex lasts 20+ years without degrading
Easy to fit — slit tube design snaps over existing pipework without disconnecting anything

Standard grey foam pipe lagging (polyethylene foam) is cheaper but has a higher thermal conductivity and degrades faster, particularly in damp conditions. For serious freeze protection, Armaflex is the right choice.

What Thickness Armaflex Do You Need?

The colder and more exposed the location, the thicker the insulation you need. As a practical guide for freeze protection:

Pipe Size	Location	Recommended Wall Thickness
15mm–22mm	Loft space, moderate exposure	13mm
15mm–22mm	External run, severe exposure	19mm–25mm
28mm–35mm	Loft space, moderate exposure	19mm
28mm–35mm	External run, severe exposure	25mm–32mm
42mm–54mm	Any unheated location	25mm

When in doubt, go thicker — the cost difference between 13mm and 19mm wall is small compared to the cost of a burst pipe. Read our full Armaflex thickness guide for detailed guidance.

Where to Fit Armaflex for Freeze Protection

Loft Spaces

Cold water storage tanks, expansion vessels and all pipework in unheated loft spaces should be insulated. Pay particular attention to pipes near the eaves where cold air infiltrates most readily. Insulation should extend from the tank connections all the way down to where the pipes enter the heated space below.

External Wall Penetrations

Where pipes pass through external walls, the wall itself creates a cold zone. Insulation should extend well into the heated space on both sides of the wall to prevent localised freezing at the penetration point.

Condensate Pipes

Boiler condensate pipes are one of the most common causes of boiler breakdown in cold weather. External condensate runs must be insulated — use Armaflex with a weatherproof finish for any exposed external section. Read our dedicated condensate pipe insulation guide for full details including how to thaw a frozen condensate pipe.

Outdoor and External Pipework

Garden tap supply pipes, external heating pipework and any pipe running in an unheated outbuilding or garage needs insulation. For fully exposed outdoor runs, standard Armaflex needs UV protection — use Armaflex Tuffcoat or cover with aluminium jacketing. Read our outdoor pipe insulation guide for the right products.

How to Fit Armaflex — Step by Step

Choose the right size — the bore of the insulation must match the outside diameter of the pipe. For 15mm copper pipe, use 15mm bore Armaflex. Read our pipe sizing guide if unsure.
Cut to length — use a sharp knife and cut squarely. Slightly long is better than short.
Apply adhesive to the seam — apply Armaflex 520 adhesive to both faces of the longitudinal slit. Allow to become touch-dry (2–5 minutes).
Snap over the pipe — open the slit and snap the insulation over the pipe, then press the seam closed firmly along its full length.
Seal butt joints — apply adhesive to both faces of every joint between lengths. Unsealed joints are gaps in the insulation.
Cover fittings and valves — use Armaflex sheet cut to shape to cover any exposed fittings. A gap at a fitting is a freeze point.

Read our full Armaflex installation guide for detailed instructions including how to insulate bends and fittings.

Frequently Asked Questions

At what temperature do pipes freeze?
Pipes can begin to freeze when the surrounding air temperature drops to 0°C, but in practice most freezing occurs during prolonged cold snaps of -5°C or below, particularly overnight when heating is off. Pipes in unheated loft spaces are most vulnerable.

How long does Armaflex last?
Properly installed Armaflex lasts 20+ years indoors. For outdoor installations, use Armaflex Tuffcoat or protect with jacketing to prevent UV degradation.

Can I fit Armaflex myself?
Yes. Armaflex is designed for straightforward installation. The slit tube snaps over existing pipework without disconnecting anything. The main requirement is using the correct adhesive on all seams and joints.

My condensate pipe keeps freezing — what should I do?
Fit Armaflex insulation on the external condensate run immediately. For a frozen condensate pipe right now, pour warm (not boiling) water over the frozen section to thaw it, then reset the boiler. Read our condensate pipe guide for full details.

Is Armaflex better than standard foam pipe lagging for freeze protection?
Yes. Armaflex has a lower thermal conductivity and a closed-cell structure that does not absorb moisture. Standard polyethylene foam degrades in damp conditions and provides less effective freeze protection, particularly in exposed locations.