A laboratory apparatus has been constructed to subject fiberglass insulation to one-dimensional moist airflow and heat transfer with temperatures from 20 to -20 degrees C. Using this apparatus, the effects of air exfiltration and infiltration on the heat and moisture transport characteristics within a medium density fiberglass insulation material are investigated experimentally for one-dimensional transient conditions. The experimental results, which are typical of cold climate building envelope applications, indicated that the adsorption process had a significant influence on the temperature distribution over much of the warm portion of the slab during air exfiltration shortly after the tests began. Furthermore, for all of the air exfiltration tests carried out, the majority of the moisture and frost accumulation was within the insulation slab adjacent to the cold surface. For air infiltration, it was discovered that the drying rate was substantially higher for lower airflow rates.