Every mainstream insulation type in one honest table — performance, real installed costs, and the application each is actually suited to. No universal winner: suitability is application-dependent.
| Type | Best for | λ W/mK | Typical cost | Thickness for job | Moisture notes | Fire | DIY? | Lifespan |
|---|---|---|---|---|---|---|---|---|
| Mineral wool quilt | Lofts at joist level | 0.038–0.044 | £18–£28/m² installed | 270mm | Breathable; keep eaves vented | A1 non-combustible | Yes | 40yr+ |
| Fibreglass quilt | Lofts (budget) | 0.040–0.044 | £18–£26/m² | 270mm | Breathable | A1 | Yes | 40yr |
| PIR board | Rafters, floors, flat roofs | 0.022–0.028 | £45–£75/m² fitted | Half the thickness of quilt | Vapour control needed | Combustible (Class varies) | Partly | 50yr |
| Blown cavity fill | Suitable cavity walls | 0.034–0.040 | £14–£22/m² | 50–100mm cavity | Survey for exposure/damp | A1 (mineral) | No | 25yr CIGA |
| EWI system | Solid walls (outside) | system 0.030–0.038 | £95–£135/m² | 90–120mm | Moisture design critical | System-rated | No | 30yr+ |
| IWI (insulated board) | Solid walls (inside) | 0.022–0.038 | £60–£95/m² | 60–100mm | Junction/moisture design | Varies | Partly | 30yr |
| Multifoil | Rafter build-ups (space-limited) | system-dependent | £30–£55/m² | Thin | Only as part of designed system | Varies | Partly | 25yr |
| Wood fibre | Breathable retrofits, floors | 0.038–0.043 | £40–£80/m² | Thicker | Excellent moisture buffering | B–C | Partly | 40yr |
Lower λ (lambda) = better insulator per mm — but cost, moisture behaviour and the application decide the right choice, not lambda alone. PIR wins where depth is tight; mineral wool wins on cost and fire for lofts; EWI/IWI are wall systems, priced accordingly. “Best” only means best for the job — our Best Insulation guide walks each application.
Installed costs above are EST-anchored (May 2026) at 0% VAT. Most measures are fundable for eligible households via ECO4 or WH:LG — see the UK Insulation Price Index for the full dataset with methodology.
AC-coupled (battery has its own inverter) is the retrofit default: no rewiring of your array, works with any brand or age of system, £3,500–£6,000 installed for 5–10kWh usable. DC-coupled only makes sense if your inverter is due replacement anyway — a hybrid inverter + battery swap can be cheaper combined.
Feed-in Tariff payments are unaffected by adding storage — generation payments continue and deemed export isn’t metered down. On SEG, a battery lets you shift export into peak-price windows instead.
Match usable capacity to your evening consumption and summer surplus — the sizing guide has the tables. Most 4kWp homes land at 5–8kWh usable.
There's no universal winner — mineral wool leads for lofts, blown fill for suitable cavities, EWI/IWI systems for solid walls, PIR where space is tight. Application decides.
Mineral wool/fibreglass quilt at £18–£28/m² installed — and it's the right choice for most lofts, not just the cheapest.
Loft quilt and suspended-floor rolls. Cavity fill, EWI, IWI and spray systems are professional-only.
Energy Saving Trust benchmarks (May 2026) plus stated assumptions — full methodology on our UK Insulation Price Index.
Facts checked 21 August 2026. We link to official sources and show when facts were last verified. If a scheme changes, we update the page.
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