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This guide compares two popular 90mm full-fill cavity boards — EcoTherm Eco-Cavity 90mm and RECTICEL Eurowall+ 90mm — with two common 100mm cavity batts: URSA 32 100mm and Superglass Superwall 32 100mm. The aim is to help builders, renovators and self-builders decide which system best suits their project, balancing thermal performance, cost, and installation practicality.
90mm cavity boards (rigid PIR or phenolic boards) typically deliver lower thermal conductivity per millimetre, are cut to exact sizes and are often supplied tongue-and-groove for a tight fit. 100mm cavity batts are flexible glass-mineral wool slabs that can be easier to compress into irregular cavities and are usually cheaper per m² but have a slightly higher λ (thermal conductivity) value.
| Product | Form | Nominal Thickness | Typical λ | Strengths |
|---|---|---|---|---|
| EcoTherm Eco-Cavity 90mm | Rigid board (PIR) | 90 mm | ≈ 0.022 W/m·K | Consistent panel sizes, foil-faced, tongue & groove, full-fill with residual cavity, cost-effective for PIR boards. |
| RECTICEL Eurowall+ 90mm | Rigid board (PIR) | 90 mm | ≈ 0.022 W/m·K | Tongue & groove edges, installer-friendly, good moisture and long-term stability. |
| URSA 32 100mm Cavity Batt | Flexible batt (glass mineral wool) | 100 mm | ≈ 0.032 W/m·K | Lower cost, flexible to fit irregular cavities, widely available. |
| Superglass Superwall 32 100mm | Flexible batt (glass mineral wool) | 100 mm | ≈ 0.032 W/m·K | Low cost, flexible to fit cavities, widely available. |
Boards such as EcoTherm Eco-Cavity and RECTICEL Eurowall+ have lower thermal conductivity per mm, which means a 90 mm board can deliver comparable or better U-values than a thicker mineral-wool batt. This is valuable when internal space is limited or when trying to hit U-value targets without increasing wall build-up.
Full-fill boards are cut to consistent sizes (1200 × 450 mm typical) and often have tongue-and-groove edges that reduce gaps and cold bridging—helpful for airtightness and predictable performance. They also require careful fixing and must maintain a small residual cavity (~10 mm) for moisture management.
Cavity batts like URSA 32 and Superglass Superwall 32 are flexible and easier to push into uneven cavities; they tolerate minor variations in cavity width but need careful placement to avoid gaps, compression, or sagging which reduces performance. Batts are often cheaper per pack and can speed up fitting in large-scale projects.
PIR boards are rigid, water-resistant (foil facings) and dimensionally stable; they are not susceptible to settling. Glass mineral wool batts are treated for water repellency and are non-combustible in the fibre form, but the overall system performance depends on correct detailing (ties, cavities, trays, and vents). Superglass slabs highlight recycled content and BRE Green Guide ratings which can be a spec advantage.
Batts generally offer the lowest upfront cost per m² — ideal for budget-constrained projects — while boards carry a premium but deliver higher performance per mm and simplified, consistent installation. Choosing boards can avoid the need for extra thickness, which is beneficial where space is at a premium.
Notes: thermal conductivity values are approximate and install quality and detailing will affect actual performance. Always check the official product datasheet and install according to manufacturer instructions and Building Regulations.
