Briquette is a building wall component, which is widely used in developing countries. This study, supported by the State Planning Organization of Turkey, aims to improve the thermal insulation characteristic of the wall briquette by adding hazelnut shells to its mortar. For this purpose, briquette specimens, which consist of pumice, sand, cement and various ratios of hazelnut shell, have been prepared and the thermal conductivity of the specimens has been measured in conjunction with parameters such as temperature, humidity, etc. The results obtained show that the thermal conductivity of the specimens decreases with increasing ratio of addition of hazelnut shells under all circumstances. (c) 2004 Elsevier Ltd. All rights reserved.