EXIBA - EUROPEAN EXTRUDED POLYSTYRENE INSULATION BOARD ASSOCIATION

Main characteristics:

   » Thermal conductivity and thermal transfer resistance
   » Water Absorption
   » Compressive strength and compressive creep
   » Dimension stability
   » Behaviour at low temperatures
   » Behaviour under radiation
   » Natural weathering behaviour
   » Durability against chemicals and solvents
   » Durability against micro organisms
   » Vermin and rodent resistance
   » Fire protection performance


	Thermal conductivity and thermal resistance The thermal conductivity of XPS depends among others on the thickness of the boards and typically lies in a range between 0.03 and 0.04 W/mK. Producers of XPS boards provide detailed values. Links to the website of our member companies are listed on the home page of this site. XPS’s thermal conductivity is tested on conditioned samples according to EN 12667 or EN 12939. Using the procedure described in EN 13164, the manufacturer’s CE marking declares a thermal conductivity λ_D, detected from a statistically procedure of all measurements from the different productions. XPS products produced with a blowing agent displaying a lower thermal conductivity than air and remaining in the foam for a certain period are tested according to the artificial aging procedure as described in EN 13164, Appendix C. The manufacturer declares thermal resistance R_D per product and rated thickness. These values are also detected from a statistically procedure of all measurements from the different productions according to the procedure described in DIN EN 13164 by rounding down in 0,05 m²K/W steps.

Water Absorption
The closed cell structure of the XPS foam makes capillary water absorption impossible. But water vapour movement is possible through XPS foam.

Water absorption behaviour is tested according to three main test procedures:

Long term water absorption by immersion according to EN 12087

Long term water absorption by vapour diffusion according to EN 12088

Freeze-thaw resistance according to EN 12091.

Water absorption by immersion
XPS is tested in a water bath of 23°C. The test duration is 28 days. XPS may not absorb more than 0.7 Vol.-% water. The CE-declaration for water absorption by immersion according to EN 13164 is WL(T)0,7.

Water absorption by diffusion
XPS sample is placed above a water bath with 50°C and a cooling disc with 1 °C. Both sides have a relative humidity of 100%. This results in the XPS boards’ exposure to both, a high temperature difference as well as a high water vapour partial pressure difference. The testing time is also 28 days. The insulation boards are turned every 7 days. Not more than 3 - 5 Vol.-% water may be absorbed during this test. The CE-declaration according to EN 13164 allows two levels WD(V)3 or WD(V)5. Dependant on the board thickness the water absorption by diffusion is between 0,5 and 3 Vol.-% in case of level WD(V)3 and between 1,5 and 5 Vol.-% in case of level WD(V)5. We know from practical experience with XPS that 20 to 30 years after their installation in strongly humid structures the actual humidity values are lower than those obtained during the diffusion test.
The diffusion test has thus turned out to be an effective testing method over time.

Freeze-thaw resistance
XPS samples already used during the diffusion test continue testing with 300 freezing and thaw cycles between -20°C and +20°C. XPS may not have absorbed more than 1 Vol.-% water in addition to the diffusion test. The CE-declaration for freeze-thaw resistance according to EN 13164 is FT1 in case of less than 2% water absorption after 300 freeze-thaw cycles additional to the diffusion test or FT2 in case of less than 1% additional water absorption after this test.

Water vapour transmission
The water vapour diffusion resistance factor µ is tested according to EN 12086 and declared according to EN 13164 in levels between 300 and 50 as MU300 respectively MU50. The higher factors are for thinner boards and the lower factors for the thicker boards.

Compressive strength and compressive creep
Compressive strength and compressive creep are important building material characteristics. They indicate the limits of the material for short and long term load.

Compressive strength or compressive stress at 10 % deformation
Compressive strength or compressive stress at 10 % deformation are limit values for shortterm load and tested according to EN 826.

The XPS manufacturers label this values according to EN 13164 in the CE-coding e.g. CS (10\Y) 300 in case of a compressive strength or compressive stress at 10 % deformation of at least 300 kPa.

Compressive creep
Compressive creep is the limit value for long-term load. The materials behaviour is tested according EN 1606. Permitted long-term pressure loads range from 60 to 250 kPa for the various XPS grades.

The manufacturers use the CE-coding of EN 13164, e.g. CC (2/1,5/50)180. This means that the allowed long-term load for this grade is 180 kPa. During the application time of 50 years this foam may not be compressed by more than 2% with the partly creep deformation of less than 1,5 %.

XPS has an elastic behaviour at uneven or non-homogenous grounds. It has no brittle fracture tendencies. Localised loadings are therefore absorbed via local deformations.

Dimensional stability
Compressive strength and compressive creep are important building material characteristics. They indicate the limits of the material for short and long term load.

Dimensional stability under specified temperature
EN 1604 serve to detect dimensional stability at specified temperature, e.g. 70°C for 48 h storage time. The manufacturers CE-declaration is DS(T+) if the foam fulfils the requirements of relative changes in length, width and thickness of less than 5%.

Dimensional stability under specified temperature and humidity conditions
EN 1604 serve also to detect dimensional stability at specified temperature and humidity, e.g. 70°C and 90% relative humidity for 48 h storage time. The manufacturers CE-declaration is DS(TH) if the foam fulfils the requirements of relative changes in length, width and thickness of less than 5%.

Dimensional stability under specified compressive load and temperature conditions
Deformation under specified compressive load of 20 kPa and a high temperature of 80°C for 48 h would be determined according to EN 1605. The manufacturers CE-declaration is DLT(1)5 if the foam fulfils the requirements of relative changes in length, width and thickness of less than 5%.

The deformation under specified compressive load of 40 kPa and a temperature of 70°C for 168 h would also be determined according to EN 1605. The manufacturers CE-declaration is DLT(2)5 if the foam fulfils the requirements of relative changes in length, width and thickness of less than 5%.

Temperature range in applications
The limit temperatures of rigid polystyrene foam materials in applications range from -180°C up to +75°C for standard grades and +85°C for special grades.


	Behaviour at low temperatures For rigid polystyrene foam applications in the construction industry and in refrigeration engineering, there are practically no lower temperature limits. Experiences are available for low temperature applications down to -180°C. But due to the thermal expansion behaviour, the dimensional changes resulting from extreme temperature changes must be taken into account.


	Behaviour under radiation Solar radiation e.g. UV- radiation and roentgen radiation, cause surface erosion effects at polystyrene foams. In practice, XPS therefore has to be covered with coatings, protective layers, laminations, etc. to protect from long-term radiation exposure.


	Natural weathering behaviour Due to its low water absorption XPS needs no measures to prevent it from precipitation water. But in flat roof application for example, protection from UV-radiation, wind uplift forces and hail can be achieved by supporting XPS, with an at least 5 cm gravel layer.


	Durability against chemicals and solvents In practice, thermal insulating materials are used in contact with adhesives, coatings, solvents, release agents, bitumen products, concrete etc. It is therefore essential to pay attention to their chemical resistance to these substances. XPS boards are for example resistant to construction materials such as lime, cement, plaster, bitumen, saline solutions, diluted acids and leaches. They are however non-resistant to fuel, tar products, lacquer solidifiers and other solvents.


	Durability against micro organisms. XPS foams are no culture medium for micro organisms. They don’t rot, moulder, or de-cay. Micro organisms can however settle in case of surface contamination with dirt. Increased temperatures and air humidity’s increase that risk. The insulation material itself remains however unaffected during these biological events. The humid acid resistance of XPS for any applications in contact with soil has been proved.


	Vermin and rodent resistance If rodents or insects encounter polystyrene foam during foraging, or during their own construction of shelters or on escape routes, the foam can be damaged. Mechanical protective layers, such as wire mesh, perforated plates, etc. can minimise the risk for especially endangered areas. For applications in barns, regular cleaning of the foam boards can significantly lower the risk of insect attacks.

Fire protection performance
As all other organic substances, XPS is combustible. If a flame retardant is used, XPS is classified in the harmonized European fire classification scheme E when tested as a product alone. If the product is tested simulating the end-use application in a construction, better classifications can be achieved.

Ignitability and flame propagation
Polystyrene foams start to soften and shrink from 100°C. They melt at even higher tem-peratures. If the melted mass gets further heated, ignitable decomposition gases are created at about 350°C. Without a flame source and temperatures above 450 to 500°C lead to the ignition of the decomposition products. Up to these temperatures, polystyrene foam is not self-ignitable.

When exposed to a small,flame, the flame retarded XPS melts away from the ignition source without itself igniting. Ignition of the foam can only be observed after longer flame exposures. If the contact with the external flame stops, neither further burning nor smouldering can be observed.

In conjunction with other combustible substances possessing less advantageous fire protection characteristics, even flame retarded polystyrene foam can burn.

Emissions from XPS involved in fire
Biological studies of acute inhalation toxicity yielded the result that the smouldering and combustion gases could be attributed solely to carbon monoxide.. The effects of combustion from XPS foam are not more acutely toxic than the effects of combustion from common building materials such as wood.