Physical properties for bark and xylem of twigs of yerba mate were analyzed to use them in a mathematical model for describing the drying of composite materials. Shrinkage coefficient and apparent density depended on moisture content and were found to be different for both regions. Equilibrium moisture contents for different water activity values were measured at temperatures between 30 and 90 C. Desorption moisture isotherms varied with the type of material and with temperature. Between 30 and 60 C, the GAB model exhibited the better fit to the sorption data, while in the range 70-90 degreesC, experimental data were better described by the Halsey's model. Equilibrium moisture content between xylem and bark could be described through a potential function, which did not depend on temperature. (C) 2004 Elsevier Ltd. All rights reserved.