C-Therm Blog

Thermal Conductivity of XPS (Extruded Polystyrene) Foam

Polystyrene foams are good thermal insulators and are therefore often used as building insulation materials.  Extruded polystyrene foam (XPS) consists of closed cells and offers improved surface roughness, higher stiffness and reduced thermal conductivity. The image below illustrates application of the insulative material in a typical home construction.  XPS is applied in this case in enhancing the performance of the insulating system for a framed ceiling assembly.

XPS insulaiton in typicaly home ceiling installation

As the thermal conductivity of the XPS material is a key quality performance attribute - manufacturers and customers are regularly looking for an easy means of obtaining the thermal conductivity performance data on the material..  Recently a European manufacturer of the XPS material sent some samples to our lab for characterization with the C-Therm Thermal Conductivity Analyzer.  The manufacturer sent several sample coupons.  (IMPORTANT: although the manufacturer  of the XPS samples cut the samples to smaller dimensions  than the typical XPS board dimensions - they need NOT have been - the TCi system can easily handle larger sample formats - ultimately the samples were sized due to shipping considerations. )  

Testing setup followed a pretty typical setup in placing the smaple on the sensor as pictured below.  An extension plate (TCi accessory) was used to better support the sample on the sensor.  For larger samples the sensor would have been inverted on the test sample.  The sample was tested from both the top and bottom in assessing the homogeneity / consistency of the sample.  

Thermal Conductivity Measurement of XPS (Extruded Polystyrene)

Testing results for the sample were available within 10 minutes in testing both the top and bottom of the sample and are summarized in the table below:

 

XPS Thermal Conductivity Testing Results (W/mK)
  Top Bottom
1 0.0334 0.0341 
2 0.0344 0.0342 
3 0.0341 0.0342 
4 0.0343  0.0340 
5 0.0340 0.0340
Average 0.0341 0.0341

 

Testing results established the material to be of excellent consistency and in close agreement for the expected thermal conductivity range of the material.  All testing was done at ambient conditions (approximately 24 deg C).  Specifications for the TCi Thermal Conductivity Analyzer offer an accuracy of <5% and a precsision <1%.  

 

Links:

WikiPedia Page on Polystyrene

Extruded Polystyrene Foam Association

XPS Manufacturers:  Knauf Insulation,  URSA Insulation, Dow Building Solutions, Owens Corning

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