  Systematic studies on the GEM foil material are performed to measure the
moisture diffusion rate and saturation level. These studies are important
because the presence of this compound inside the detector's foil can possibly
change its mechanical and electrical properties and, in such a way, the
detector performance can be affected. To understand this phenomenon, a model is
developed with COMSOL Multhiphysics v. 4.3, which described the adsorption and
diffusion within the geometry of GEM foil, the concentration profiles and the
time required to saturate the foil. The COMSOL model is verified by
experimental observations on a GEM foil sample. This note will describe the
model and its experimental verification results.
