Spray foam, blown bead or mineral wool batts: the right insulation for each part of your home

If you've had an installer turn up and tell you spray foam is the answer to everything, this page is the counterweight. Three insulation methods dominate UK retrofit work in 2026 — spray foam (open-cell or closed-cell PU, applied to roof undersides or stud walls), blown bead (EPS beads injected into a cavity), and batt-form quilt (mineral wool or sheep wool rolls between joists or studs). Each has a clear best-fit use. Picking the wrong one wastes money at best — and at worst, in the case of spray foam fitted in some lofts, can quietly damage your ability to sell or remortgage the property.

Quick comparison

Open-cell spray foam — where it earns its keep

Density 7–14 kg/m³, expands around 100× to fill irregular cavities. Excellent acoustic damping (used in recording studios for a reason), good thermal performance (R-value around 3.7 per inch), vapour-permeable so it doesn't trap moisture. Best applications: stud walls in renovations, between rafters in garden offices, party wall insulation. Not recommended in unventilated loft voids — the vapour permeability becomes a humidity-management headache.

Closed-cell spray foam — the mortgage-lender problem

Density 32–48 kg/m³, much denser, vapour-impermeable, structurally rigid. Bonds to the substrate and adds compressive strength. Excellent thermal performance (R-value around 6.5 per inch). Then the issue: sprayed onto the underside of roof tiles in an unventilated loft, it can hide rotting battens, prevent inspection, and trap moisture against the timber. Most major UK lenders since 2023 won't lend on a property with closed-cell spray foam in the loft. Removal is £40–£90/m² in our 2026 pricing — we do it all the time for homeowners trying to sell.

Blown bead cavity wall insulation — the quiet workhorse

EPS beads (or graphite-EPS for about 10% better thermal performance) blown into the cavity through 22mm holes drilled in the mortar joints. Single-day install, no internal disruption. Industry-standard with a 25-year insurance-backed CIGA guarantee. ECO4 and GBIS both fully fund this for eligible households. Removable via vacuum extraction if ever needed. For about 95% of UK cavity wall retrofits, this is simply the right answer.

Mineral wool batts and rolls — the classic

The backbone of UK loft and stud insulation. Knauf Earthwool and Isover are the two big brands. Class A1 non-combustible fire rating, vapour-permeable, recyclable, and the cheapest option per m² by a wide margin. Best applications: open loft floors (between joists + cross-laid over the top), stud partition walls, internal ceiling voids. Fully ECO4 and GBIS fundable for eligible households.

A simple decision tree

1. Cavity wall? → blown bead (almost always).
2. Open loft with full headroom? → mineral wool quilt.
3. Stud partition wall, garden office, soundproofing? → open-cell spray foam or mineral wool batts.
4. Tight rafter depth, room-in-roof, headroom-critical? → multifoil (a separate product, not spray).
5. Sealed structural panel reinforcement (commercial)? → closed-cell spray foam.
6. Existing spray foam in the loft and trying to sell or remortgage? → call us about removal before anything else.

For a free survey that recommends the right method for each part of your home — not a one-product-fits-all sales pitch — book online or ring 0800 229 4094. No cost. No obligation. No pressure.