A Guide to Insulation Values

Proper insulation can significantly impact a building’s energy consumption and promote comfortable indoor temperatures. However, when deciding the right insulation material, insulation values play a huge role.


In this article, we will delve into the world of insulation values, exploring their types and how they vary from material to material.

What Are Insulation Values?

Insulation values are numerical measures to assess how well a material resists heat flow. These values are important for determining how effective insulation material is in minimising heat transfer between the inside and outside of a building and come into play when dealing with the ultimate range of metal insulation.


Three main types of insulation values are commonly used:


  • U-value
  • R-value, and
  • K-value.

U-value (Thermal Transmittance)

The U-value represents the heat transfer rate through a specific material or assembly. It measures how effectively an insulation material prevents heat from moving through it. U-values are used to assess the heat loss or gain rate in entire building components, such as walls, roofs, and windows. Generally, a lower U-value indicates better insulation performance.

R-value (Thermal Resistance)

The R-value of a material measures its ability to resist heat flow. It’s the reciprocal of the U-value, and a higher R-value indicates better insulation. R-values are commonly used in regions with colder climates, as they help determine the appropriate insulation thickness needed for a specific application.

K-value (Thermal Conductivity)

The K-value represents a material’s intrinsic ability to conduct heat. It’s the measure of heat transferred through a unit area of a material when there’s a temperature difference of one degree Celsius between its two sides. Lower K-values indicate better insulating materials.

Factors Affecting Insulation Values

Several factors influence the insulation values of materials and building components:


  • Material type: Different materials have varying thermal properties. For instance, fibreglass, cellulose, foam, and mineral wool offer different insulation levels.
  • Thickness: Thicker insulation generally leads to higher R-values and lower U-values
  • Density: Higher-density materials often provide better insulation due to reduced air movement within the material
  • Moisture: Moisture can significantly reduce the insulation effectiveness of certain materials
  • Installation quality: Even the best insulation material can underperform if not properly installed, leading to gaps and thermal bridges
  • Environmental conditions: Temperature, humidity, and wind speed can impact insulation performance over time.

Insulation Values of Various Materials

Here is a table showcasing the insulation values of some commonly used insulation materials in the UK, including the ultimate range of metal insulation:


Insulation Material U-Value (W/m²K) Range R-Value (m²K/W) Range K-Value (W/mK) Range
Mineral Wool 0.030 – 0.040 2.5 – 3.3 0.035 – 0.040
Expanded Polystyrene Foam Insulation (EPS Insulation) 0.030 – 0.038 2.6 – 3.3 0.030 – 0.040
Extruded Polystyrene Foam Insulation (XPS Insulation) 0.028 – 0.038 2.6 – 3.6 0.028 – 0.038
Polyisocyanurate Insulation (PIR) and Polyurethane (PUR) Foam 0.022 – 0.028 3.6 – 4.5 0.022 – 0.028
Cellulose Insulation (Recycled Paper Fibers) 0.036 – 0.042 2.4 – 2.8 0.036 – 0.042
Reflective Foil Insulation (Multifoil) 0.036 – 0.040 2.5 – 2.8  
Phenolic Foam 0.018 – 0.028 3.6 – 5.6 0.018 – 0.028


Note that these values are approximate and can vary based on factors like product formulation and manufacturer.

How to Choose the Right Insulation Value

Choosing the right insulation value for your building is an important decision that can significantly impact energy efficiency, comfort, and long-term costs. Here are a few tips for choosing the right insulation value:

Understand Local Climate

Cold climates typically require a higher R-value to prevent heat loss, while hot climates may prioritise insulation that prevents heat gain. Therefore, consider your immediate environment’s temperature ranges, humidity levels, and seasonal variations.

Determine Building Type

Different types of buildings have varying insulation requirements, depending on their use -residential, commercial, industrial- and their material -metal, concrete, wood. For example, a concrete office building will likely have different insulation needs than a metal warehouse.

Identify Building Components

Each building component might have different insulation needs based on its exposure to the elements. You should, therefore, identify the parts of your building that need insulation -walls, roofs, floors, windows, and doors.

Research Appropriate R-Values

Each area has local building codes that provide guidelines for minimum insulation requirements. These codes consider climate and building type to suggest appropriate R-values. Carry out the necessary research to determine your area’s recommended R-values.

Consider Insulation Types

Different insulation materials have varying R-values and performance characteristics, as displayed in the table above. Research materials like fibreglass, cellulose, foam, and mineral wool to determine which values best align with your needs.


Understanding insulation values is essential for creating energy-efficient and comfortable buildings. Choosing the right materials based on their insulation values and ensuring proper installation can equip your building with the insulation needed to maintain optimal indoor temperature conditions and conserve energy.

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