Evaluation of previous measurements of water vapor sorption in wood at multiple temperatures

Water vapor sorption is a fundamental physical property of wood and has numerous implications for the behavior of wood as a building material. As a result, water vapor sorption isotherms have been studied for over a century and are the topic of countless publications. Despite their importance and depth of study, there has not yet been a thorough review of these studies that can be used to guide readers to the highest quality sorption data. Sorption data acquired at multiple temperatures are frequently used for thermodynamic analysis or to validate sorption models. This review summarizes all known papers where water vapor sorption isotherms have been measured on wood at three or more temperatures and includes 27 studies published from 1930 to 2018. For each study, the quality of the data is evaluated from the experimental details listed in the publication. One of the essential details is the operational definition of equilibrium, often specified as a threshold for change in mass with time. Unfortunately, upon close examination of the methods, definitions of equilibrium in many cases were not specified or were lacking in stringency, which calls into question the accuracy of the data. In the end, only three of the 27 studies are recommended as being reliable for thermodynamic analysis or for validating sorption isotherm models.