The use of structural insulated panels (SIPs) for wall and roof assemblies in residential and commercial buildings is a well-known construction technique. SIPs typically use a combination of either expanded polystyrene foam (EPS) or polyurethane foam (PUR) as the core material. The covering or skin is predominantly oriented strand board (OSB). The OSB is either bonded to the foam with adhesive in the case of EPS, while polyurethane is used to provide adhesion with PUR SIPs. This paper presents the results of research that investigated the use of industrial hemp mat used as a skin for soy-based polyurethane foam panels. A series of tests were conducted to investigate moisture resistance and flexural behaviour on hemp mat foam panels. Moisture absorption behaviour was evaluated on three specimen types: uncoated, earth plaster and tung oil treated hemp mat. The absorption coefficient Aw was determined for all specimens. The tung oil treated specimens exhibited a water absorption coefficient that was 5.3% of that for untreated hemp mat panel specimens. Flexural tests were conducted on dry specimens with earth-plastered hemp mat, tung oil coated hemp mat, OSB and, untreated hemp mat skins. Tung oil provided resistance to tension failure and increased capacity to withstand considerable deformation without tensile failure in flexural specimens. Compared with pure foam specimens, untreated hemp mat improved flexural performance by 16.3%.