Pitched Roof Insulation Between Rafters: Is SuperFOIL SF19+ the Best Option?

SuperFOIL SF19+ vs Rockwool

Rockwool is the traditional choice for between-rafter insulation, and for good reason — it’s affordable, fire-resistant, and has decades of proven performance behind it. But it comes with trade-offs that SF19+ was designed to solve.

To hit modern Building Regulations U-values with rockwool alone, you typically need 150mm–200mm of depth between and often below the rafters. On many older Suffolk roofs, that depth simply isn’t there — or it comes at the cost of headroom you can’t afford to lose in a loft conversion.

SF19+, by contrast, achieves strong thermal performance at a fraction of the depth. Its <cite index=”6-1″>nano coating technology improves performance from a slim, high-tech foil solution</cite>, meaning you can hit comparable or better U-values without eating into your ceiling height. Rockwool also has no inherent vapour control or air-tightness layer — it needs a separate membrane fitted correctly to avoid condensation risk, whereas SF19+ builds that in as standard.

Rockwool wins on: raw material cost, simplicity, and acoustic performance. SF19+ wins on: space efficiency, built-in vapour control, and ease of installation in one product.

SuperFOIL SF19+ vs PIR/Foam Boards (e.g. Celotex, Kingspan)

Rigid PIR boards offer very high thermal performance per millimetre and are a common choice for rafter insulation on newer roofs. Where they fall down is on-site practicality: every board has to be individually measured and cut to fit between irregular rafter spacings, which on older Suffolk roofs — where rafters are rarely perfectly uniform — leads to gaps, thermal bridging, and wasted material.

SF19+’s flexible quilt <cite index=”3-1″>conforms easily to irregular surfaces and structural junctions</cite>, which makes it far more forgiving to install cleanly on older or non-standard roof structures, with less wastage and fewer cold spots caused by poor-fitting joints.

PIR boards win on: raw thermal performance per millimetre, and rigidity for load-bearing situations. SF19+ wins on: installation speed, adaptability to awkward roof structures, and reduced thermal bridging at joints.

SuperFOIL SF19+ vs Sheep’s Wool

Sheep’s wool is the natural, breathable option, prized for its ability to regulate moisture and its lower environmental footprint. It’s an excellent choice for period properties and anyone prioritising sustainability above all else.

Where it differs from SF19+ is depth and vapour handling. Sheep’s wool needs meaningful thickness to perform, similar to rockwool, and — being a breathable material — it works best as part of a “breathable” roof build-up rather than a fully sealed one, which needs to be planned carefully to avoid interstitial condensation. SF19+’s built-in vapour control layer takes that variable out of the equation, and its slim profile suits situations where depth is at a premium.

Sheep’s wool wins on: sustainability credentials and breathability in period properties. SF19+ wins on: slim profile, integrated vapour control, and installation speed.