The Shower – Thermal Conductivity of Shampoo and Conditioner

MP-2 with THW-L3


This is the second part in a series of blog posts where we investigate the thermal conductivity of liquids found in many households. Part one is found here and part three is coming soon. We use the Thermtest THW-L3 sensor and the portable Measurement Platform Two, MP-2, for all these tests. By experimenting with various liquids, we try to show that it can be both easy and fun to test thermal conductivity with the Transient Hot Wire method. The affordable and portable MP-2 device is both powerful and versatile and suitable for research, teaching, and product development in the field of thermal conductivity!

In this second chapter we investigate two liquids found in the Thermtest Europe bathroom: Shampoo and Hair Conditioner from the brand Barnängen.

Measurements and equipment

Testing was performed at room temperature, approximately 22 °C, and the tested sample volumes were roughly 15 ml. The instrument configuration was MP-2 and ASTM D7896-19 compatible sensor THW-L3. Default THW-L3 test parameters were used, and optimum heating power was determined by the instrument. Since both conditioner and shampoo contain a lot of salt and therefore have has a relatively high electrical conductivity, the temperature probe on the sensor was coated to prevent erroneous temperature readings.

THW-L3 sensor with MP-2 and shampoo and conditioner
Figure 1. Samples, THW-L3 sensor and MP-2 handheld. Shampoo left and conditioner right.

The easy to work with MP-2 instrument with the THW-L3 thermal conductivity sensors can be operated by experienced scientist and layman alike. Simply pour the sample into the sample holder and dip the probe in it so that the entire wire is submerged. Then wait for thermal stability in the sample and run the 1 s transient test. In less than 1 minute from starting the test you will have a result. Testing can also be automated by scheduling several tests. It’s also possible to connect the device to a PC and control the testing from the companion software, which also allow easy export of the data to Excel for further analysis.

Results and discussion

Table 1. Thermal conductivity of Hair conditioner and shampoo. Data as measured with the MP-2 handheld and THW-L3 sensor. Presented thermal conductivity data are average values of three repeated tests and the related standard deviation.




Hair Conditioner

0.575 W/m/K

0.83 %


0.541 W/m/K

0.92 %

Distilled Water (Controlled)

0.608 W/m/K

0.47 %

In addition to testing shampoo and conditioner, distilled water was analysed to confirm sensor calibration and the data quality. The results from water were within 1 % of the expected value.

Hair conditioner and Shampoo are both water-based fluids, and as such it’s not surprising that the thermal conductivity is not very far from that of water. The additives then reduce the thermal conductivity to different extent. We can also see that the standard deviation, while still being very small, it’s still larger than for the water. This is likely a result if the high electrical conductivity of the samples which can have a small impact on measurement stability.

The MP-2 platform

The MP-2 is as the name indicates a platform for several transient methods of testing thermal conductivity. The methods currently featured include Transient Plane Source (TPS), Transient Line Source (TLS) and Transient Hot Wire (THW).

MP-2, thermal conductivity probes
Figure 2. The MP-2 and its thermal conductivity probes.

The TPS method is represented by two sensor types, TPS-4 for testing thermal conductivity and TPS-EFF for testing thermal effusivity. The former operates as described in ISO 22007-2 with some modifications to fit the portable format and the latter operated in accordance with ASTM D7984.

The TLS method is represented by no less than four needle type sensors. TLS-100, TLS-50, TLS-150 and TLS-100 vCp. TLS-100 is the classic 100 mm long ASTM D5334 probe for testing soil. TLS-50 allows convenient testing of hard samples through its 50 mm length and increased 4 mm diameter. TLS-150 is 150 mm long and adds the IEEE 442-2017 standard for soil testing while also following ASTM D5334. Finally, the unique TLS-100 vCp measures thermal diffusivity in addition to thermal conductivity, which in turn allows the calculation of the specific heat per unit volume – all this by still following ASTM D5334.

The THW method is represented by two probes, the THW-L3 for liquids, pastes, and powders and the THW-S for testing insulation, soft materials, and powders.