To better understand the similarities and differences between moisture and volatile organic compound (VOC) diffusion through porous media, a dual chamber experimental system was developed. The diffusion and partition coefficients of moisture and selected VOCs in materials were compared. A pilot test with gypsum wallboard and oriented strand board (OSB) showed similar diffusion kinetics between moisture and VOC. To further establish the similarity relationship between VOC and water vapor transport, calcium silicate was used as a reference material to develop the concept of a similarity coefficient and its application in combined heat, air, moisture and pollutant simulation (CHAMPS) in buildings. The diffusion resistance factor calculated for moisture from the dual chamber tests agreed well with that from the conventional dry cup test method. The diffusion behavior of each particular VOC in porous media is predictable as long as the similarity coefficient of the VOC is known. Future experiments will extend this to materials with significant VOC emissions in buildings.