Phenolic foam insulation
Guide to energy retrofit of traditional buildings, published by Historic Environment Scotland in November 2021, defines phenolic foam as: ‘A synthetic polymer made from thermosetting foam plastic and used in thermal insulation’
Phenolic foam is considered one of the best material for thermal insulation.
- It has over 90% closed cell formation, giving it good stability.
- Phenolic foams come in varying densities in the range of 35 kg/m³ to 200 kg/m³. High density varieties such as insulation boards have good strength and are suitable for floor insulation.
- It has low thermal conductivity. The thermal conductivity of phenolic closed cell insulation material is generally between 0.018 W/m.K and 0.023 W/m.K.
- It has fire retardant properties and a low smoke level (even under pyrolysis).
- It is water resistant.
- It is lightweight and so is easy to transport and install.
- Closed cell phenolic insulation foam can resist almost all inorganic acidic erosion, organic solvents and acids. However, it under-performs in alkaline environments.
- When exposed to sunlight for long periods it does not show any noticeable ageing.
- Insulation boards show good sound absorption properties.
The most common blowing agent used in phenolic foam insulation is ‘Pentane’. This is used to comply with EC regulation, because it is CFC and HCFC free, has no ozone depletion potential and low global warming potential. Pentane is a hydrocarbon. In order to prevent the blowing agent escaping and being replaced by air, the insulation boards are covered with gas tight aluminium foil or glass tissue.
Illustrated Guide to Mechanical Building Services 3rd Edition (BG 31/2017), written by David Bleicher and published by BSRIA in May 2017, suggests that phenolic foam is: ‘A solid foam insulation with good thermal performance that can be used on most systems. As with mineral wool insulation, if used on cold water, chilled water or refrigeration pipework, it must be vapour sealed to reduce the risk of condensation forming on the pipe surface.’
[edit] Related articles on Designing Buildings
- Aerogel insulation for buildings.
- Cavity wall insulation.
- Conduction.
- Fire retardant.
- Heat transfer.
- Interstitial condensation.
- Phase change materials.
- Polyurethane spray foam in structurally insulated panels and composite structures.
- Solid wall insulation.
- Sound insulation.
- Thermal bridge.
- Thermal comfort.
- Transparent insulation.
- U-value.
Featured articles and news
We're expanding our collaborative mission by launching DB Intelligence, an exclusive market research advisory panel. Built environment professionals can now get paid to share their expertise on industry trends, products and services.
Panel members receive direct financial incentives for participating in research projects like short surveys, 1-2-1 interviews and focus groups. Register today to shape the future of the construction sector.
Planning condition discharge in England and Wales
A brief exoplanation from a building compliance expert, with further links.
Overheating guidance and tools for building designers
Guidance for dealing with element of building fabric control that have increasing importance.
Shading for housing, a design guide
From the Good Homes Alliance and British Blind and Shutter Association.
UK Standard Skills Classification (SSC)
A shared framework for describing skills needs.
Social media ban consultation comes to close
CIOB urges UK Government to consider social media’s role in careers guidance in ban debate.
The latest of eight Skills England apprenticeship units
The addition of battery manufacturing welcomed by ECA with a warning about the risks of fast-tracked apprenticeship units.
Building Control Independent Panel final report
A precis of a key report led by Dame Hackitt with full recommendations and link to the government response.
Building Safety recap April, 2026
A short and longer run-through of the month, with links to further information and sources.
CIAT May 2026 briefing.
From medieval scribes to modern word art.
ECA welcomes crackdown on late payment and push for clean energy, whilst CIOB seek fixed cladding removal timeframes.
Cyber Security in the Built Environment
Protecting projects, data, and digital assets: A CIOB Academy TIS.
Managing competence in the built environment
ITFG publishes new industry guide on how to meet the ICC principles.
The UK's campaign to reduce noise pollution: Mythbusting, articles and topic guides.