25mm Kingspan Kooltherm K5 External Wall Board

25mm Kingspan Kooltherm K5 is a premium external wall insulation board engineered for superior thermal performance on masonry walls. Built with a fibre-free rigid thermoset phenolic core, this board delivers exceptional energy efficiency for external wall insulation systems and thin coat rendering applications.

The 25mm K5 board works seamlessly with both conventional and lightweight polymer-modified renders. Installation takes place entirely from the outside, allowing you to upgrade external walls on occupied properties without internal disruption.

As one of the market's thinnest external wall insulation board (EWI) options, it maximises usable internal space—making it the perfect solution for buildings where internal insulation isn't practical.

This 25mm board features mineral glass facings bonded to the insulation core during manufacture and delivers a certified thermal conductivity (lambda) of 0.022 W/mK. The phenolic core provides outstanding thermal efficiency whilst being manufactured with a blowing agent that has zero Ozone Depletion Potential (ODP) and minimal Global Warming Potential (GWP).

Kingspan Kooltherm K5 25mm satisfies Building Regulations requirements through superior thermal performance in a reduced thickness. It achieves higher insulation values with a thinner profile than comparable EPS, XPS, and mineral wool products.

Each board measures 1200mm x 600mm x 25mm, delivering a lightweight, manageable product that's straightforward to fit.

Product specification

• Brand: Kingspan
• Model: 25mm K5 Single Board
• Thickness: 25mm
• Length: 1200mm
• Width: 600mm
• Weight: 0.57kg
• Dimensions: 1,200mm x 600mm x 25mm
• Board Coverage: 0.72m2 per board
• Pack Coverage: 0.72m2
• Pack Quantity: 1 board
• Compressive Strength: 100kPa
• Density: 35kg/m3
• Thermal Conductivity: 0.022 W/mK
• R-Value: 2.50m2K/W
• Material: Rigid thermoset phenolic insulation
• Profile: Square edge
• Colour: Light shade of red
• Fire Classification: Euroclass C-s2,d0
• Finish: Mineral glass coatings
• Application Temperature: from +5 °C to +25 °C
• Applications: External insulation for masonry walls
• BBA Certified: Yes
• Features: Thinnest commonly used External Wall Insulation Board
• Manufacturer: Kingspan Kooltherm® K5

Application

Install Kooltherm K5 boards according to manufacturer specifications, which outline comprehensive design and installation procedures. For best performance, attach boards to the substrate (masonry or timber) using Premium Basecoat adhesive combined with metal screw mechanical fixings.

After securing boards to the external wall, apply a protective outer layer—either a mortar basecoat or netting cover—to guard against excessive heat, moisture, and UV damage. Complete the installation with a protective render topcoat. Consult our detailed installation guide for comprehensive step-by-step instructions.

Storage Instructions

Shelf Life: Refer to the manufacturer's expiry date. Storage Conditions: Store in a dry location, in the original packaging, and away from excessive heat or UV light.

Applications

• External wall insulation systems
• Solid brick and block walls
• Cavity block and brick walls
• Thin coat rendering
• Cavity brick walls
• Cavity dense block walls
• Insulated render systems
• Steel-framed walls
• Timber-framed walls

Kingspan Kooltherm K5 Installation

We recommend

1. Adhesive and Base-Coat Render: EWI-225 Premium Basecoat Render Adhesive 25kg,
2. Rendering Mesh: Orange Fibreglass Rendering Mesh Roll,
3. Priming Paint: EWI-333 Top Coat Primer,
4. Top Coat Thin Coat Render: EWI-075 Silicone Render.
5. Plastic Fixings: 70mm Insulation Panel Fixings Plastic Pin,
6. Metal Fixings: 70mm Insulation Panel Fixings LMX10 Metal Pin Hammer Fix,
7. Base Track: 25mm Aluminium Base Track | 2500mm length profile,
8. Render Beads and Profiles

What is Phenolic Insulation?

Kingspan K5 Phenolic insulation, including our Kooltherm range, ranks among the most thermally efficient insulation materials on the market. Manufacturing involves a specialised process that creates a rigid thermoset foam core sandwiched between two facing layers, such as low-emissivity composite foil.

Choosing phenolic insulation enables you to reach low target U-values using minimal insulation thickness, making it an excellent choice for projects demanding high performance and space efficiency.

Info

Browse our complete Kingspan Products range and refine by thickness or coverage using the left-hand filters. To discuss product suitability for your project or request a quantity discount quotation, contact us by phone on +4402038839057, email sales@insulationbee, or use Live Chat for the lowest UK Kingspan insulation prices.