U Value Calculator
Colour Picker
Find an Installer
Contact Us

Phenolic insulation is manufactured by a process in which a plastic foam forms an insulating core between two flexible tissue faced layers. It has a high closed cell content and fine cell structure.

Rigid phenolic insulation is produced by mixing high solids and phenolic resin with a surface acting agent. The heat created by the reaction evaporates a volatile liquid blowing agent in the mixture which produces a network of small bubbles in the material. The foam can be cured to create one of two forms of the product. It can be manufactured by a continuous process to create thin sheet material which is laminated with various facings and cut into boards.

Phenolic Insulation – Thermal Performance

Rigid phenolic insulation products offer very good thermal insulating properties due to the very low thermal conductivity of phenolic foam, compared with rigid polyurethane or extruded polystyrene. It can actually be 50% more effective than other common insulation materials. Its low thermal conductivity allows specified thermal performance targets to be achieved with minimal thickness of insulation. This is particularly significant where space saving is important.

Physical Qualities of Phenolic Insulation


Rigid Phenolic insulation has a high closed cell content and fine cell structure. It is lightweight, easy to transport , handle and install. The core of Kingspan Kooltherm® K5 is a premium performance rigid thermoset fibre-free phenolic insulant manufactured with a blowing agent that has zero Ozone Depletion Potential (ODP) and low Global Warming Potential (GWP). Kingspan Kooltherm® K5 is faced on both sides with a glass tissue based facing, adhesively bonded to the insulation core during manufacture.

  Compressive Strength

The compressive strength of Kingspan Kooltherm® K5 typically exceeds 100 kPa when tested to BS / I.S. EN 826: 2013 (Thermal insulating products for building applications. Determination of compression behaviour).

  Material Resistance

Rigid phenolic insulation is resistant to fungus and mould growth and will not sustain vermin.

  Heat Resistance

Rigid phenolic insulation can withstand continuous temperatures of up to 120 degrees C.

  Moisture Resistance

Moisture has a minimal effect on its thermal performance. Rigid phenolic insulation has a 95% (or greater) closed cell content which makes it highly resistant to moisture penetration. It also has a low water vapour permeance. Phenolic foam is also non-wicking. This means that if water enters the insulation system due to the vapour barrier becoming punctured, any moisture ingress is limited and confined to the punctured area. This ensures moisture does not build up and compromise the whole system.


Rigid phenolic is dimensionally stable and can be cut accurately to achieve a snug fit in situations such as between rafters where airtightness will be improved.


Rigid phenolic insulation is non- biodegradable but waste material can be put back into the manufacturing process for reuse.

Thermal Properties of Phenolic Insulation

The λ-values and R-values detailed below are quoted in accordance with BS / I.S. EN 13166: 2012 + A2: 2016.

Thermal Conductivity

The boards achieve a thermal conductivity (λ–value) of:

  • 0.021 W/m.K (insulant thickness >45 mm);
  • 0.022 W/m.K (insulant thickness 25–44 mm).

Thermal Resistance

Thermal resistance (R–value) varies with thickness and is calculated by dividing the thickness of the board (expressed in metres) by its thermal conductivity. The resulting number is rounded down to the nearest 0.05 (m2.K/W).

Insulant Thickness Thermal Resistance


Responsible Sourcing

Kingspan Kooltherm® K5 – produced at Kingspan Insulation’s Pembridge, Herefordshire manufacturing facility – is certified to BES 6001 (Framework Standard for the Responsible Sourcing of Construction Products) ‘Excellent’.

Kingspan Kooltherm® K5 produced at Kingspan Insulation’s Pembridge, Herefordshire and Castleblayney, Co. Monaghan manufacturing facilities is manufactured under a management system certified to ISO 14001: 2015.

The above information is correct at the time of writing. Please confirm at the point of need by contacting Kingspan Insulation’s Technical Service Department (see rear cover), from which copies of Kingspan Insulation’s certificates can be obtained

NBS Plus

  For NBS Plus Information, click here: NBS Plus

Fire Performance

There are potential restrictions placed upon this product which vary dependant on building type, height, construction and location in Great Britain. For guidance regarding the routes to compliance for meeting the fire safety requirements of the Building Regulations / Standards in Great Britain, refer to the relevant Technical Bulletins and links to Government websites at www.kingspaninsulation.co.uk/fireregulations.

Kingspan Kooltherm® K5 achieves European Classification (Euroclass) C-s2,d0 when classified to EN 13501-1: 2018 (Fire classification of construction products and building elements. Classification using data from reaction to fire tests). Kingspan Kooltherm® K5 in a specific construction has been successfully tested to BS 8414-1: 2015 + A1: 2017 (Fire performance of external cladding systems. Test method for non-loadbearing external cladding systems applied to the masonry face of a building). The specific construction must be followed when using the performance-based route as a route to compliance in England, Wales and Scotland. The end use design needs to be carefully considered to replicate the design details used in the tested construction. For details of how to access the test report please visit www.kingspan.com/gb/bs-8414-systems (UK) or https://www.kingspan.com/irl/en-ie/product-groups/ insulation-boards/kooltherm/kooltherm-k15-rainscreenboard (Ireland), or further information can be provided by emailing highrisetechnical@kingspan.com (UK) or technical@kingspaninsulation.ie (Ireland).

Further details of the fire performance of Kingspan Insulation products may be obtained from the Kingspan Insulation Technical Service Department.

    Please fill out the form below, your download will automatically start. Your download will also be available via email in case it doesn't automatically start.