Take a closer look at Celotex XPS 300 FN insulation
To mark the trial launch of the new Celotex XPS 300 SL FN floor insulation boards in select CCF branches across the UK, we are taking a more detailed look at this exciting new range.
What is Celotex XPS 300 SL FN?
Manufactured by Soprema Insulation Ltd under the Celotex brand, Celotex XPS 300 SL FN is a rigid thermal insulation board made from extruded polystyrene (XPS) foam.
Where can it be used?
In demanding applications such as beneath ground bearing slabs, high-load floors, basements, or underground structures, insulation can be required to do more than only retain heat. It can also be required to resist moisture, withstand loads, and perform reliably over the long term.
Celotex XPS 300 SL FN has been designed for these applications. With its closed-cell structure, tested low water absorption, and compressive strength of 300kPa at 10% deformation (EN 826), it can be specified in environments where both thermal insulation and load resistance are required.
Typical applications include use above or below ground bearing concrete slabs, suspended slabs, and internally or externally to basements. It can also be installed above or below damp proof membranes, in projects with high moisture exposure or load demands, and in challenging environments such as basements, car parks, and swimming pools.
What are the key product features?
Celotex XPS 300 SL FN offers a thermal conductivity of 0.032 W/mK, helping designers achieve required U-values with slimmer build-ups compared to materials with higher thermal conductivity. Its compressive strength of 300kPa at 10% deformation also means it can be specified in higher load floor applications such as basements or commercial projects.
The shiplap edge profile creates tight joints that reduce thermal bridging and help prevent water tracking. Thanks to its low water absorption and closed-cell structure, the product retains insulation integrity in moist conditions, supporting use in below-ground and damp environments. Available in a choice of board thicknesses and formats to meet different U-value requirements and site constraints, the range is certified by BBA with all technical information available at https://celotex.co.uk/products/celotex-xps-300-sl-fs
How easy is it to work with?
Very and here is a best practice guide for installing Celotex XPS 300 SL FN above ground-bearing concrete slabs.
Prepare the substrate Ensure the base is level, clean and stable. Lay suitable damp proof membrane above or below the slab.
Lay boards tightly Use the shiplap edges to maintain close joints. This helps avoid thermal leakage or water ingress.
Apply a vapour control layer An AVCL is installed on the warm side of the insulation to limit inhibit the risk of condensation.
Check perimeter detailing Fit edge strips or perimeter insulation to avoid thermal bridging.
5.Install screed or topping Apply the overlying layers following manufacturer guidance for thickness and curing.
Protect from moisture Maintain continuity of damp proof membranes and ensure proper drainage at junctions.
Why choose CCF?
The trial launch of Celotex XPS 300 SL FN at select CCF branches reflects our ongoing commitment to providing high-performance insulation solutions for a wide range of construction applications. By partnering with leading manufacturers like Celotex, we continue to support the evolving needs of the UK construction industry with products that deliver reliability, flexibility, and technical performance. Plus our in-house insulation team is always on hand to help guide you through our extensive range of solutions.
To explore availability near you, visit our branch locator: https://www.ccfltd.co.uk/branch-locator