This paper is a synthesis of the various research projects studied by our research laboratory over the period 1974 to 1982 on the general topic of moisture.The various points covered by these projects, concerning exclusively mineral fiber insulations, are:# water vapor fixation mechanisms# vapor-barrier# moisture effect on heat transferAs a result of this work, we are able to assess that:# glass fibrous insulations with currently used binders are not hygroscopic# the vapor-barrier may be omitted in numerous applications# the effect of moisture on the thermal resistance of fibrous insulations can be considered as negligible in most building applications.