The European norm of reference of the product "Extruded Polystyrene - XPS" is EN 13164 and the European norm of reference of the "Polyurethane - PU" is EN 13165.

These norms enumerate the tests that must be done to the products, already be obligatory as optional. In these norms also are indicated the dimensions that must have the samples to test, the frequency in which the tests must be done, as well as the classification of the products on the basis of the results obtained of every test.

In case of the thermal conductivity, the European norm specifies that the producer must do, annually, a statistics with all the results of thermal conductivity obtained every day of the internal control of the production.

The value of the statistics is the value that the manufacturer must declare and write in the Declaration of Conformity CE. For this motive, every manufacturer is obliged to present the Declaration of Conformity CE of the product.

The value of thermal conductivity, in most cases, is different according to be calculated in the moment of the production or after several days or weeks. Normally, the value of the thermal conductivity increases with the time until this one becomes stable. The latter value (stable value) is the aged value.

Definitively, we are interested in the aged value, since ** the manufacturer has to declare the value of the conductivity that the material will have in the moment of his installation and along his life in the building**.

The time of aging, after which the thermal conductivity of the product is calculated, is defined in the norm of every product:

- For the PU, the test will be realized 175 days after production

- For the XPS:

a. For thickness from 20 mm to 70 mm, the test will be realized 90 days after production

b. For thickness from 80 mm to 120 mm, the test will be realized 50 days after production

c. For thickness >120 mm, the test will be realized 30 days after production

The manufacturer must have, at least, ten results of thermal conductivity tests, obtained by means of internal measures (or external). With these results, the manufacturer must calculate the declared value.

The thermal conductivity value, obtained of the statistics, must round up, exactly 0,001 W/mK and the manufacturer will declare this value in intervals of 0,001 W/mK. For example, if the result of the statistics is 0,033645 W/mK, the declared value must be 0,034 W/mK.

The **Thermal Conductivity** is a physical property of the materials that it measures the aptitude to pass, across it, the heat. The thermal insulation is a material very used in the construction and it is characterized for being a barrier to the pass of the heat.

**A good thermal insulation is characterized for having a low thermal conductivity **(a few quantities of heat passes across it). For example, we have two thermal insulations of the same thickness, one of them with thermal conductivity 0,034 W/mK and the other, 0,036 W/mK. The best thermal insulation will be the one that has minor thermal conductivity, in this case, the one that has 0,034 W/mK.

The Thermal Resistance of a material is the capacity of the material to being opposed to the heat flow. **A good thermal insulation has a high thermal resistance.** If we have two thermal insulations of the same thickness, the best thermal insulation will be the one that major thermal resistance.

The thermal resistance depends on the thickness and on the thermal conductivity of the material:

Thickness (m)

Rt = ------------------------------------------------- (Units: m^{2}K/W)

Statistic Thermal Conductivity (W/mK)

The thermal conductivity value obtained must round down, exactly 0,05 m^{2}K/W, and the manufacturer will declare this value in intervals of 0,05 m^{2}K/W. For example, a thermal insulation has thickness 80mm and a thermal conductivity of 0,036 W/mK, the thermal resistance calculated is 2,22 m^{2}K/W, and the declared value will be 2,20 m^{2}K/W.