Mr. Hart will summarize the results of several hygrothermal analyses, using commercially available software, on simulated insulated chilled water pipe, held at a fixed temperature for 25 years in a Houston, Texas ambient environment. The pipe insulation modeled was a highly porous mineral fiber material with each of four different sheet-type vapor retarder jackets. These jackets had water vapor permeance values from a high of 0.134 perm to a low of 0.005 perm. The results show significant differences in predicted quantities of water vapor condensation and in subsequent increases in insulation thermal conductivity between each of the four insulation systems.