Armaflex vs Rockwool Pipe Insulation — Which Should You Choose?

June 7, 2026

Armaflex and Rockwool are two of the most widely used pipe insulation materials in the UK, but they are fundamentally different products suited to different applications. Choosing the wrong one for your project can result in condensation problems, fire compliance failures or premature insulation failure.

This guide compares Armaflex and Rockwool pipe insulation across every factor that matters to engineers, contractors and specifiers.

What is Armaflex?

Armaflex is a flexible, closed-cell elastomeric rubber foam pipe insulation manufactured by Armacell. It is the world's most widely specified elastomeric pipe insulation and is the default product for HVAC, refrigeration and plumbing pipework in the UK. Its closed-cell structure gives it excellent vapour resistance, making it the standard choice for condensation control on cold pipework.

Browse Armaflex pipe insulation at Pipelagging.

What is Rockwool Pipe Insulation?

Rockwool (also known as mineral wool or stone wool) pipe insulation is made from spun volcanic rock fibres formed into rigid or semi-rigid pipe sections. It is manufactured by Rockwool International and several other companies. Rockwool pipe insulation is used primarily on high-temperature pipework, industrial systems and applications where fire performance is the primary specification criterion.

Armaflex vs Rockwool: Head-to-Head Comparison

Fire Performance: Class O vs Non-Combustible

This is the most significant technical difference between the two products.

Armaflex Class O achieves Class O under BS 476, which is the highest surface spread of flame classification. It will not significantly contribute to the spread of fire across its surface. However, it is a combustible material — it will burn if subjected to a direct flame.

Rockwool is non-combustible — it achieves Euroclass A1, meaning it does not contribute to fire at all. It will not burn, melt or produce smoke even when subjected to direct flame. This makes Rockwool the correct choice for applications where non-combustibility is a specification requirement, such as fire-rated ductwork, plant rooms with strict fire compartmentation requirements and some industrial applications.

For most standard HVAC and plumbing applications in the UK, Class O (Armaflex) is sufficient. Non-combustibility (Rockwool) is required only where specifically called for in the project specification or fire strategy. Read our guide to insulation fire ratings for full details.

Condensation Control: A Critical Difference

This is where Armaflex and Rockwool differ most significantly for cold pipework applications.

Armaflex has a closed-cell structure with a water vapour resistance factor (µ) exceeding 7,000. Water vapour cannot penetrate the insulation and reach the cold pipe surface, preventing condensation. This is why Armaflex is the standard specification for chilled water, refrigeration and air conditioning pipework.

Rockwool has an open-fibre structure with very low vapour resistance (µ of 1–5). Water vapour passes freely through the insulation and condenses on the cold pipe surface beneath. On cold pipework, Rockwool without a vapour barrier facing will rapidly become saturated with condensation, losing its thermal performance and causing corrosion on the pipe.

Rockwool should not be used on cold pipework without a factory-applied or site-applied vapour barrier facing. Even with a vapour barrier, the risk of condensation at joints and penetrations is significantly higher than with Armaflex.

For any application where condensation control is important — chilled water, refrigeration, cold water supply — Armaflex is the correct choice. Read our condensation on pipes guide for more details.

Temperature Range: Where Rockwool Wins

Rockwool's major advantage over Armaflex is its high-temperature capability. Standard Armaflex is rated to +105°C, with Armaflex HT Solar rated to +150°C. Rockwool pipe insulation is available in grades rated to +300°C, +450°C and beyond, making it the only practical choice for steam pipework, high-temperature process pipework and industrial applications above 150°C.

For standard heating systems (flow temperatures up to 80°C), both products are technically suitable on temperature grounds. For steam and high-temperature industrial pipework, Rockwool is required.

Installation: Flexibility vs Rigidity

Armaflex is highly flexible and can be fitted to straight runs, bends, valves and fittings without specialist tools or fabricated sections. It is slit along its length and snapped over the pipe, making it fast to install even on complex pipework layouts. Read our Armaflex installation guide for full details.

Rockwool pipe sections are rigid and are supplied as pre-formed half-sections that are wired or banded around the pipe. Bends, valves and fittings require fabricated sections or mitred cuts, which is more time-consuming. Rockwool installations typically also require metal jacketing or cladding to protect the mineral wool and provide a finished surface, adding further installation time and cost.

Which Applications Suit Each Product?

Cost Comparison

For standard pipe sizes and wall thicknesses, Armaflex and Rockwool pipe insulation are broadly comparable in material cost. However, the total installed cost of Rockwool is typically higher because:

Rockwool installations usually require metal jacketing or cladding, adding material and labour cost
Fabricating bends and fittings in Rockwool takes longer than fitting flexible Armaflex
Rockwool requires banding or wiring to hold sections in place during installation

For most standard HVAC and plumbing applications, Armaflex offers a lower total installed cost as well as superior condensation control performance.

Summary: Which Should You Choose?

Choose Armaflex if:

You are insulating cold pipework (chilled water, refrigeration, cold water supply)
The pipe operating temperature is below 105°C (or 150°C with HT Solar)
You need a self-finishing installation without jacketing
You are working on HVAC, plumbing or air conditioning pipework
Class O fire rating is sufficient for the specification

Choose Rockwool if:

The pipe operating temperature exceeds 150°C (steam, high-temperature process)
Non-combustibility (Euroclass A1) is a specification requirement
You are working on industrial or process pipework above Armaflex's temperature rating

Frequently Asked Questions

Can Rockwool be used on cold water pipes?
Rockwool is not recommended for cold water pipes without a vapour barrier facing. Its open-fibre structure allows water vapour to pass through and condense on the cold pipe surface. For cold pipework, Armaflex is the correct choice.

Is Armaflex better than Rockwool?
For most HVAC, plumbing and refrigeration applications, Armaflex is the better choice because of its superior condensation control, flexibility and self-finishing properties. Rockwool is better for high-temperature and non-combustible applications where Armaflex cannot be used.

Can I use Armaflex on steam pipes?
Standard Armaflex is rated to +105°C and is not suitable for steam pipework. Armaflex HT Solar is rated to +150°C. For steam systems above 150°C, Rockwool or another high-temperature insulation is required.

Does Rockwool need jacketing on pipe insulation?
In most applications, yes. Rockwool pipe insulation requires metal jacketing or cladding to protect the mineral wool fibres, provide a finished surface and prevent water ingress. This adds to the installation cost and time compared with self-finishing Armaflex.