The samples were conditioned using a moisturizing apparatus and their k-values were measured at different moisture content levels and mean operating tem- peratures. A state-of-the-art heat flowmeter apparatus was utilized to measure the k-value. Measurement data were analyzed utilizing linear regression to quantify the impact of moisture content and to establish the relationship between the k-value of different types of fibrousinsulating materials with various mass densities and the level of moisture content over the hygroscopic and wetting ranges