Structural insulated panels (SIPs) are gradually gaining popularity as an alternative construction material for residential and light commercial buildings in the UK. They show marked advantages in strength, thermal performance and speed of installation when compared with the traditional timber frame method of construction. While many types of composite panel building systems have been developed, panels made from a thick layer of foam (often expanded polystyrene) sandwiched between two layers of oriented strand board (OSB) or plywood are usually referred to as SIPs. They were developed in North America and although they have experienced wide-scale utilisation around the world, the concept is still relatively unknown in the UK. This paper details part of a comprehensive research study on SIPs at Napier University and deals with their performance under combined bending and axial compression and the effects of medium-term loading on panel integrity for use as load-bearing walls and columns. The results have illustrated that SIPs perform as an effective composite material possessing considerable strength and stiffness necessary to sustain required design loads.