Alternative Insulation Materials: What to Know Before You Choose
An overview of natural and other insulation materials, where each is typically used, and the checks that matter as much as the material itself: a proper survey, a moisture risk assessment and a competent installer.
What Breathable Insulation Can and Cannot Do
Suits traditional walls
Brick, stone, earth and lime walls absorb and release moisture. Permeable (vapour-open) insulation and finishes help avoid trapping moisture in them.
Not a fix for existing damp
Wall and loft insulation should not go in until damp problems and exterior repairs such as pointing, roofs and gutters have been dealt with.
Ventilation still matters
Insulation changes how air and moisture move. Airbricks, wall vents and trickle vents should not be blocked, and extra ventilation may be needed.
Check with your lender about spray foam
RICS advises checking with your lender before installing spray foam, and some lenders will not lend where it is in the roof. Keep all paperwork and guarantees for any insulation you install.
Insulation Materials Compared
Sheep's Wool Insulation
Natural fibreWool fibre supplied as rolls or batts. It is hygroscopic, meaning it can take up and release moisture vapour, which is why it is often used in traditional and breathable constructions.
✓ Advantages
- • Can buffer moisture vapour
- • Renewable material
- • Useful acoustic performance
- • Can be cut and fitted between timbers
Considerations
- • Usually costs more than mineral wool, so get quotes
- • Check the product has been treated against moths and other insects
- • Check the fire classification and certification of the product
- • Does not fix an existing damp problem
Often used for: Lofts, between timbers in roofs and timber frame walls, breathable internal wall build-ups
Check: For lofts, ask the supplier what depth gives performance equivalent to the 270mm of mineral wool that the Energy Saving Trust says building regulations recommend.
Wood Fibre Board Insulation
Natural fibre boardRigid or flexible boards made from wood fibre. The boards are vapour-open, and rigid boards can take a render or plaster finish as part of a compatible system.
✓ Advantages
- • Vapour-open, so it suits permeable wall build-ups
- • Can be used externally with a compatible render or internally on traditional walls
- • Denser than most insulation, which can help slow summer heat gain
- • Renewable material
Considerations
- • Needs to be thicker than foam boards for the same insulating value
- • Must be used as part of a compatible system of boards, fixings and finishes
- • Needs protecting from rain during installation
- • Specialist installation needed
Often used for: External and internal insulation on traditional solid walls, roofs, timber frame construction
Check: The Energy Saving Trust puts typical external wall insulation at around £15,000 and internal wall insulation at around £12,000 for a typical 3-bed semi in Great Britain. Ask for the system certificate.
Aerogel Insulation Blankets
Thin, high-performanceFlexible blankets or boards containing aerogel, a very lightweight material with low thermal conductivity. Its main use is where there is very little room for insulation.
✓ Advantages
- • Thin for its insulating value
- • Useful in tight spots such as window and door reveals
- • Keeps loss of room size to a minimum with internal wall insulation
- • Water-repellent products are available
Considerations
- • Expensive compared with most insulation materials
- • Can be dusty to cut and handle, so follow the manufacturer's guidance
- • Moisture behaviour and fire classification vary by product
- • Professional design and installation needed
Often used for: Thin internal wall insulation, window and door reveals, places where space is very limited
Check: Ask for independently tested thermal and fire performance for the specific product and system.
Mineral Wool (Stone Wool or Glass Wool)
Common choiceRock or glass spun into fibres. It is one of the most widely used materials for loft insulation and is among the common loft materials listed by the Energy Saving Trust.
✓ Advantages
- • Widely available
- • Many products are non-combustible (check the product rating)
- • Vapour-open
- • Good acoustic performance
Considerations
- • Can irritate skin, eyes and airways when handled, so wear protection
- • Loses effectiveness if squashed, for example under loft boards
- • Leave a ventilation gap if boarding over it
- • Must be kept dry to perform
Often used for: Lofts, timber frame walls, cavity wall insulation (as blown fibre), sound insulation
Check: Energy Saving Trust loft costs in Great Britain: around £750 to lay 270mm from nothing, or £600 to top up from 120mm to 270mm, which saves about £17 a year.
Hemp Fibre Insulation
Natural fibreBatts or rolls made from hemp plant fibre, often combined with other fibres or binders. Like other natural fibres it is hygroscopic and suits breathable constructions.
✓ Advantages
- • Plant-based, renewable material
- • Can buffer moisture vapour
- • Useful acoustic performance
- • Can be cut and fitted between timbers
Considerations
- • Less widely available than mineral wool
- • Cost varies by product, so get quotes
- • Needs a breathable construction to get the benefit
- • Check the fire classification and certification of the product
Often used for: Timber frame construction, lofts and roofs, breathable internal wall build-ups
Check: If embodied carbon matters to you, ask for the product's Environmental Product Declaration (EPD) rather than relying on marketing labels.
Multifoil Reflective Insulation
Thin reflectiveThin layers of foil separated by wadding or foam. Part of its performance comes from reflecting radiant heat, which depends on air gaps either side.
✓ Advantages
- • Thin and lightweight
- • Quick to fit
- • Can form an airtightness layer in some systems
- • Useful where depth is limited
Considerations
- • Performance depends on correct installation and air gaps
- • Manufacturer claims vary, so rely on independently tested values
- • Usually used alongside other insulation rather than on its own
- • Many products act as a vapour barrier, which does not suit every construction
Often used for: Roofs and loft conversions alongside other insulation
Check: Ask for independently tested performance for the complete roof or wall build-up, not the foil on its own.
Quick Comparison: General Considerations
| Material | Moisture behaviour | Often used for | Main thing to check |
|---|---|---|---|
| Sheep's wool | Hygroscopic, vapour-open | Lofts, timber roofs and walls | Insect treatment, fire classification |
| Wood fibre | Vapour-open | Solid walls (inside or out), roofs | A complete compatible system |
| Aerogel | Varies by product | Thin internal insulation, reveals | Tested thermal and fire data |
| Mineral wool | Vapour-open, must stay dry | Lofts, timber frame, cavities | Not squashed, ventilation kept clear |
| Hemp fibre | Hygroscopic, vapour-open | Timber frame, lofts, breathable walls | Availability, fire classification |
| Multifoil | Often a vapour barrier | Roofs, with other insulation | Independently tested values |
General guidance only. Performance, fire classification and moisture behaviour vary by product and system, so check the manufacturer's data sheet and certification for the product you are offered.
How to Choose the Right Option
Costs are typical figures from the Energy Saving Trust, not quotes. Scheme dates and grant details are from Ofgem and GOV.UK. Last reviewed September 2026.
Getting Started
Get an Independent Survey
A surveyor or retrofit assessor experienced with your type of building can check condition, moisture and suitability before you choose a material. Surveys are usually paid, so ask for a fixed price first.
Tell us about your home →Compare Quotes and Check the Installer
The Energy Saving Trust recommends getting at least three quotes. Check each installer's TrustMark registration, their insurance and who backs the guarantee.
Ask for a specialist →Check Funding and the Standards That Apply
ECO4 ends on 31 December 2026 and GBIS has closed; in England, Warm Homes: Local Grant is run by councils. ECO4 work must follow PAS 2035:2023 and PAS 2030:2023, with a Retrofit Coordinator overseeing the project, and be installed by or under a PAS 2030-certified installer and a TrustMark-registered business.
Get the Guarantee Details in Writing
Ask what guarantee applies, how long it lasts and who backs it. The Energy Saving Trust says TrustMark solid wall insulation companies offer a 25-year guarantee backed by an insurer or SWIGA, and cavity wall insulation should have a 25-year guarantee. Terms for other measures vary, so read them before signing.
Check an installer's registration on TrustMark's register. Better Home Hub does not vet or accredit installers, so make these checks yourself.
The National Audit Office (HC 1334, October 2025) found that 98% of homes with external wall insulation and 29% of homes with internal wall insulation fitted under ECO4 and GBIS had major issues requiring remediation. Before work starts:
- Ask for the retrofit assessment, the moisture risk assessment and the name of the Retrofit Coordinator
- Check the installer on TrustMark's register and ask to see their insurance
- Get the guarantee details in writing, including who backs it
- If spray foam is proposed for your roof, speak to your mortgage lender first, as RICS advises
Already have external wall insulation from ECO4 or GBIS? Use TrustMark's free Find & Fix audit first. Repairs should not cost you anything.
Want Help Finding a Specialist?
Tell us about your property. Better Home Hub may introduce a specialist who can advise on suitable insulation, and that specialist may pay us a fee.
Sending an enquiry is free. Surveys and installation are usually paid. Call 03330 505 281 or email hello@betterhomehub.co.uk.
Related Information
Sources
- Energy Saving Trust: Solid wall insulation (updated 18 June 2026)
- Energy Saving Trust: Roof and loft insulation (updated 8 May 2026)
- Energy Saving Trust: Cavity wall insulation (updated 8 May 2026)
- Energy Saving Trust: Spray foam insulation explained
- National Audit Office: Energy efficiency installations under the Energy Company Obligation, HC 1334 (14 October 2025)
- RICS: Spray foam insulation consumer guide (March 2023)
- House of Commons Library: Spray foam insulation and mortgages, CBP-10658
- Ofgem: ECO4 delivery guidance, version 4.0 (March 2026)
- GOV.UK: Extending the ECO4 end date, government response (January 2026)
- Ofgem: Great British Insulation Scheme
- GOV.UK: Apply for a Warm Homes: Local Grant
- Historic England: Upgrading thermal elements and installing insulation
Last reviewed September 2026.