Energy efficiency is the predominant criterion in green building indices, which, in turn, contributes to sustainable development. One of the materials commonly used in the insulation of buildings is foamed concrete. This investigation presents the main objective of the experimental results concerning the thermal conductivity of oil palm shell foamed geopolymer concrete (OPSFGC), utilizing waste materials such as low-calcium fly ash (FA) and palm oil fuel ash (POFA) as cementitious materials, and oil palm shell COPS) as lightweight coarse aggregate (LWA). Three OPSFGC mixtures with densities of 1300, 1500 and 1700 kg/m(3) were prepared using an artificial foaming agent; a control mix without foam and conventional materials - block and brick - were used for comparison. The test results on the mechanical and transport properties are also discussed. The thermal conductivity of OPSFGC13 of about 0.47 W/mK was 22% and 48% lower than the conventional wall materials, block and brick, respectively. OPSFGC, with a density of 1300 and 1500 kg/m3, could be categorized as structural and insulating concrete, Class-II, whereas OPSFGC with a density of 1700 kg/m3 is classified as Class-I structural grade concrete with a compressive strength and thermal conductivity of about 30 MPa and 0.58 W/mK, respectively. (c) 2013 Elsevier B.V. All rights reserved.