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.
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 Modified Transient Plane Source sensor. The manufacturer sent several sample coupons.
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 MTPS sensor can easily handle larger sample formats – ultimately the samples were sized due to shipping considerations.
MTPS Test Setup
Testing setup followed a pretty typical setup in placing the sample on the sensor as pictured below. An extension plate 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.
Experiment Results
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:
| Sample | 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 MTPS sensor offer an accuracy of <5% and a precision <1%.