"open" vs. "closed" chamber
Since the end of the 1990s, the Tewameter® has been the worldwide most used measurement principle to assess TEWL. Its “open chamber” method a number of advantages against closed chamber systems.
The experts of the EEMCO group (European group on efficacy measurement and evaluation of cosmetics and other products) confirmed this in guidelines about the important skin water measurements.
The 2018 published paper (Skin Research & Technology, 2018, 24, p. 351-358) examined all established and new methods to assess skin water content and states: .... "From skin barrier damage experiments, it became clear that the Tewameter with an open-chamber is more sensitive or disiminative and able to detect significantly smaller differences than the VapoMeter. In addition, the closed chamber device is currently not sensitive enough to measure diurnal rhythm and fluctuations of skin as a function of time. ... Thus, the closed chamber instrument is inferior to the open-chamber measurement of TEWL ...".
Does the measurement angle matter?
Not so much. It is important that the short end of the probe head sits on the skin tightly. The Tewameter® TM 300 had even successfully been used under the special condition of the ISS Space Station!
