Spanish Technical Building Code DB HE-1 states that products for walls and blind spaces on façades are defined by the following hygrometric conditions:
Thermal conductivity is a physical property which measures the insulation capacity of a material. The lower the rate, the more ability to reduce the rate of heat flow. It is an inherent property of the material, it does not have a fix value, because it depends on different factors such as temperature, density, humidity and the ageing process of the material.
Water vapour resistance factor μ.
It has to be taken into account, especially in those insulation projects which aim to preserve a cold surface. If the insulation enables the air humidity to be in contact with the cold surface, there will be condensation and it will make the insulation material wet, generating insulation capacity losses, wet surfaces and even hygienical problems and moulds.
Density ρ (kg/m3)
The volumetric mass density of a substance is its mass per unit volume.
Specific heat cp (J/kg.K)
It is the energy which results in an increase in temperature and proceeds to the transformation of other energies.