Insulation Types Compared: Which Is Right for Your Home?

An impartial comparison of UK insulation types — covering mineral wool, spray foam, rigid board, blown fibre, and external wall insulation. ## Overview There is no universally best insulation material. The right choice depends on where you are insulating, the construction of your property, your budget, and whether moisture management is a concern.

## Head-to-Head Comparison | Insulation Type | Best Location | Typical Cost | R-value per 100mm | Moisture Risk | Maintenance | |---|---|---|---|---|---| | Mineral wool (roll) | Loft floor | £5–£10/m² | 2.5 | Low | None | | Blown fibre | Loft (awkward access) | £10–£15/m² | 2.3 | Low | None | | Rigid board (PIR) | Walls, floors, flat roofs | £15–£30/m² | 4.

5 | Low | None | | Spray foam (open-cell) | Loft rafters | £20–£35/m² | 2.7 | Medium | None | | Spray foam (closed-cell) | Specialist applications | £35–£55/m² | 5.0 | Low | None | | Cavity wall beads | Cavity walls | £6–£12/m² | 2.5 | Medium | None | | EWI (external wall) | Solid walls | £80–£120/m² | 3.5+ | Low | Periodic | | IWI (internal wall) | Solid walls (interior) | £40–£70/m² | 3.

5+ | Medium | None | ## Loft Insulation **Mineral wool rolls** remain the most cost-effective insulation upgrade available. Laid between and across joists to a total depth of 270mm, they achieve the recommended U-value of 0.16 W/m²K. Government guidance recommends this as the first energy upgrade for any uninsulated home.

**Blown fibre** is useful where access is restricted or the loft space is uneven. It achieves similar performance to mineral wool. ## Wall Insulation **Cavity wall insulation** — if your property has unfilled cavities (typically post-1920s construction), filling them is one of the most cost-effective upgrades. It can be completed in a few hours with minimal disruption.

**External wall insulation (EWI)** — the most effective solution for solid-wall properties. Adds insulation boards to the exterior, finished with render. Transforms thermal performance and appearance but is a significant investment. **Internal wall insulation (IWI)** — an alternative where external insulation is not feasible (listed buildings, terraced properties).

Reduces room size slightly but avoids external alterations. ## The Spray Foam Question Spray foam is effective in specific applications but has created well-documented issues: - **Mortgage lender concerns** — some lenders refuse to lend on properties with spray foam in the loft - **Removal cost** — £3,000–£8,000+ if required - **Inspection obstruction** — can prevent visual assessment of roof timbers - **Open-cell vs closed-cell** — open-cell is lower risk for loft applications; closed-cell should be reserved for specialist use **Our guidance:** spray foam can be appropriate for rafter-level insulation where the loft is being converted to habitable space.

For standard loft insulation, mineral wool remains the safest, most cost-effective, and most mortgage-friendly choice. ## Decision Framework 1. **Uninsulated loft?** →…