The effectiveness of moisture barriers has been proved in the control of moisture changes in wood. Nevertheless coatings of wax, of aluminium paint, or of other moisture resistant material do not prevent the treated wood from attaining, eventually, a moisture content corresponding to the surrounding air. Graphs comparing the rate of moisture change in specimens of chestnut and in four small panels show what degree of dimensional stabilization of wood supports can be attained under normal climatic conditions in museums. The best moisture barriers do not prevent a significant reaction in the wood over long cycles of seasonal humidity. One curve shows the approximate reaction of wood panels in the long periods of high relative humidity which often exist in the north east of the U.S.A. Another shows a cycle of daily fluctuations in a normal uncontrolled atmosphere. Moisture barriers give excellent protection against sudden and brief changes. Constant checking of the humidity inside a museum is necessary to reasonably judge the degree of dimensional stability that one might expect from a moisture resistant coating. -- AATA