Material Thermophysical Properties

General tab on Materials Dialog.


Materials are used to define the properties of construction layers.  There are 2 types of material:


  1. Detailed properties including the thermophysical properties, surface properties and visual appearance for the material.
  2. Simple resistive material with no thermal mass.  This option will typically be used to model air gaps.


Material Thickness

Force thickness

If the material should only be used in layers of a particular thickness then check this box and enter the material thickness that applies below. When materials having this option set are selected on the Constructions dialog the layer thickness will be fixed with the material thickness described below.


This option may be useful for materials such as bricks, tiles, insulation and PCMs which are usually supplied with a particular thickness.

Note: you must check this option for materials to be used to define insulation properties within a Kiva Foundation. In this case the Default thickness value below is used to define the insulation thickness.

Default thickness

The fixed layer thickness of the material (in m or in) when selected.


This should be the dimension of the layer in the direction perpendicular to the main path of heat conduction. Modelling layers thinner (less) than 0.003 m is not normally recommended; rather, add those properties to one of the adjacent layers.

Detailed properties

Thermal bulk properties

Thermal conductivity

This field is used to enter the thermal conductivity of the material layer. Thermal conductivity must be greater than zero.


This field is used to enter the thermal conductivity of the material layer (in W/m-K or Btu-in/h-ft2-F). Thermal conductivity must be greater than zero. Modelling layers with conductivity higher than 5.0 W/(m-K) is not normally recommended.

Specific heat

This field represents the specific heat of the material layer (in J/kg-K or Btu/lb-F).

Note: EnergyPlus uses scientific SI units but data reported in textbooks and references will often use kJ/kg-K or J/g-K instead. Take care!

Only values of specific heat of 100 or larger are allowed. Typical ranges are from 800 to 2000 J/kg-K.


This field is used to enter the density of the material layer in (kg/m3 or lb/ft3). Density must be a

positive quantity.

Note: Some textbooks and references may use units of g/m3. Take care!

Simple resistance

Thermal resistance

This field is used to enter the thermal resistance (R-value) of the material layer (in m2-K/W or ft2-F-hr/Btu).

Note: Materials defined using an R-value do not contribute to construction (and hence building) thermal mass in the calculations and so should be used with care, especially if you plan to use the model for dynamic thermal simulations. You are especially advised not to use R-value materials on the innermost layer of constructions and you should not generally use them for representing materials that have mass. They are best used for modelling air gaps and insulation layers.

Vapour Resistance

You can enter vapour diffusion properties here if the material is to be used within a construction which is have a Condensation analysis carried out. This data is not used for general simulations. To include moisture diffusion in simulations you should use the Moisture transfer settings on each of the materials used in each of the constructions in the project.

Note: Vapour resistance/moisture diffusion data provided in the literature tends to be very approximate, much more so than for thermal properties. This is due to large variations in these properties that have been measured in lab tests.

Vapour resistance definition

There are 3 ways to define the vapour diffusion properties of a material:


Vapour factor

Enter the vapour factor for the material. There are no units.

Vapour resistivity

Enter the vapour resistivity, a property of the bulk material (in MNs/g.m).