Mechanical pipe insulation systems are installed on chilled water (CHW) pipes thatoperate at below ambient temperatures inside buildings. These systems generally include the useof an exterior vapor barrier film to prevent intrusion of water vapor and wetting of the insulation.When the dew point of the indoor ambient air is greater than the pipe surface temperature, watervapor is drawn from the surrounding ambient air toward the CHW pipes due to a vapor pressuredifference. Water vapor that enters the insulation systems will condense when it reaches the pipesurface. The apparent thermal conductivity of the pipe insulation systems, defined as thecoefficient kins used in this report, is affected by ambient temperature and water vapor ingressand might vary with time of service as water vapor enters the insulation systems.