Retrofitting old style steel museum cases with new improved gaskets is an economical and effective way to deal with the inadequacies of these older cabinets. By installing silicone sponge gasketry, a well-sealed cabinet is created which affords protection from the fluctuation of relative humidity as well as creating a microenvironment which does not allow the entry of dust, gaseous air pollutants, insects, vermin and light. In the old style cases, two types of gaskets have been predominantly used. These gaskets can easily be replaced and an improved door seal can be obtained for very little cost. Older storage units containing wood, however, are not acceptable, and should not be re-gasketed. The more recent polyurethane foam gaskets have been shown to deteriorate readily, primarily because of oxidation of exposure to ultraviolet radiation; they give off volatile substances as they deteriorate. These foam gaskets lose their resiliency and structural integrity in approximately 2-5 years, at which time they crumble and cause the cabinet to lose its seal.