Energy conservation has become an increasingly important issue for all sectors, particularly in industry. Therefore, the thermal performance of insulation systems and their influence on heat loss/gain in various applications in addition to economic considerations have received increased attention in recent years. In this study, a literature review of papers that addressed the optimum economic thickness of the thermal insulation on a pipe or duct with different geometries used in various industries was carried out The studies related to determining the critical insulation thickness for different geometries including circular shapes were investigated. The heat transfer equations, the basic results, the optimization procedures and the economic analysis methods used in the studies were presented comparatively. Additionally, a practical application example based on optimizing the insulation thickness on a pipe was performed, and the effective parameters of the optimum thickness were investigated. (C) 2013 Elsevier Ltd. All rights reserved.