100mm Polystyrene Insulation

100mm polystyrene insulation boards are available in both expanded polystyrene (EPS) and extruded polystyrene (XPS) and are used across floor, wall, flat roof and specialist ground applications, with this thickness frequently specified where a higher thermal performance target demands greater insulation depth than thinner boards can deliver. Insulation UK is a specialist supplier of polystyrene insulation boards and sheets, stocking a comprehensive range of EPS and XPS products at 100mm.

Types of Polystyrene Insulation Available at 100mm

EPS boards at 100mm include standard white EPS across a full range of compressive strength grades, graphite-enhanced grey EPS, and compressible clay heave protection board for ground movement applications.

XPS boards at 100mm are available from Ravatherm and Kingspan GreenGuard in multiple grades.

Applications for 100mm Polystyrene Insulation

Floor insulation is the most common application for 100mm polystyrene boards. Laid beneath a concrete slab on a well-consolidated hardcore base, 100mm EPS or XPS delivers a continuous thermal break between the ground and the finished floor, with standard EPS delivering an R-value of between 2.6 and 2.9 m²K/W depending on grade and grey EPS or XPS achieving up to 3.3 m²K/W. The boards cut cleanly with a sharp hand saw and are lightweight enough to handle without mechanical assistance, making them practical for both self-build and contractor-led projects.

In practice, the achieved U-value for the finished floor will depend on the full build-up, ground conditions and slab specification, though 100mm EPS or XPS will contribute significantly toward meeting the Part L ground floor target of 0.25 W/m²K. In projects where a wet underfloor heating system is installed over the slab, the higher performance per millimetre of grey EPS or XPS helps to keep the overall floor build-up depth manageable.

Wall insulation at 100mm suits cavity construction and internal dry-lining, and the same thickness is regularly specified for flat and inverted roof applications, particularly where XPS is laid above the waterproof membrane.

In new-build ground floor construction on clay subsoils, 100mm SPI Clayfill is frequently specified alongside standard floor insulation to absorb heave pressure before it reaches the slab.

Why Choose Insulation UK for 100mm Polystyrene Insulation?

A comprehensive range in stock across standard EPS, grey EPS, clay heave and XPS boards at 100mm, covering floor, wall, flat roof and foundation applications.

Products from trusted manufacturers including Jablite, Ravatherm, Kingspan and SPI, all available at competitive trade prices with no minimum order value.

Fast UK-wide delivery with free shipping on orders over £500 (ex VAT), and reliable nationwide logistics on every order despatched from our distribution centre in Rotherham.

Competitive pricing with some of the lowest 100mm polystyrene insulation prices available online, backed by strong stock availability and a trusted supply chain.

Expert help and advice from a team with over 50 years in the industry. Whether you are specifying a new-build ground floor slab, upgrading internal wall insulation on a period property, or sourcing clay heave boards for a development on shrinkable clay, we are here to make sure your project runs smoothly from start to finish.