The measurement of transepidermal water loss (TEWL) has been established as one of the main parameters in the assessment of skin barrier function. One of the most widely employed devices to measure TEWL is the Tewameter^®. Courage and Khazaka launched the TM300 in 2003 and successfully eliminated some of the limitations of the previous model. In the more recent device, the sensors inside the probe head can be pre‐heated to a temperature close to that of the skin, which considerably decreases sampling time. Additionally, the new technology of the probe does not require frequent and time‐consuming recalibration with different solutions. The main objective of this work was to perform a comparative assessment of the performance of the two different Tewameter^® models. Fifteen volunteers were used in this study, which was conducted in the mid‐portion of the volar forearm. The standard measurements assessed differences in the basal values, time necessary for a stable value and coefficient of variability under normal and extreme conditions. The dynamic measurements performed were based on a plastic occlusion stress test (POST), involving the application of an occlusive patch for 24 h, after which the TEWL desorption curves were recorded. A mathematical model was adjusted to the data points using a specially modified simplex routine. Calculated parameters considered relevant to the study were t_1/2evap (evaporation half‐life) and dynamic water mass (DWM). Results show slight differences in the performance the two models, which are nevertheless statistically significant. The TM300 seems to be more sensitive to differences in TEWL and presents a much quicker measurement capacity. These results confirm a marked improvement in the more recent Tewameter^® model, when compared with its predecessor. The main conclusion of this work is that caution is advised when comparing results obtained with the two different models and that studies should be carried out entirely with the same device.