Introduction

Before dealing with the principles of how insulation works and why we insulate the  buildings that we live and work in we must first have an understanding of the physics of heat transfer.

Methods of heat transfer

Heat transfer may occur due to any or all of the following methods:

• Conduction - heat transfer along or through a material including gases. Generally denser materials such as metal, concrete etc will conduct heat readily whilst gases, especially if trapped within a material, are poor conductors i.e. good insulators.
• Convection - only occurs in liquids and gases due to density differences, warm air rises and conversely cold air sinks.
• Radiation - heat energy transmitted by one object to another through space.

Remember insulation slows the processes of heat transfer - it does not completely stop it or remove the need for a heating or cooling source.

Principles of thermal insulation

All insulation materials work on the same principle of trapping air (or gas) within their structure. Polyurethane foams make use of artificial blowing agents, gases that have a better thermal performance than air, trapped within microscopic cells of the plastic. The small cell size reduces the effect of convection within the gas. Additionally the bright foil, when adjacent to an airspace, reduces the radiation heat loss thus giving an enhanced thermal performance.

Glossary of terms

• Thermal conductivity or λ-value (W/mK) - is the measure of a materials ability to conduct heat. It is an inherent physical property of that material. Lower value = better performance.
• Thermal resistance (m²K/W) - this is the next step from thermal conductivity as it introduces the thickness of the the material. It is calculated by dividing the thickness, in metres, by the thermal conductivity. Higher value = better performance.
• Thermal transmittance or U-value (W/m²K) - is the measure of the rate of heat flow through a complete floor, wall or roof element. It is calculated as the reciprocal of the sum of the thermal resistances of all the components in the element. Lower value = better performance.

Technical study of a construction element