Materials for composites play a prominent role in various applications, especially when thermal behavior is of major concern. The purpose of this review article is to consolidate research carried out in the field of low and medium temperature thermal insulators, particularly polymer-based composites which are amorphous in nature and inherently offer lower thermal conductivity; thereby the limitations of basic engineering materials in thermal resistance can be overcome by the development of different composites. Apart from thermal resistance, in comparison with conventional materials, composites offer advantages such as higher strength, durability, manufacturability, compactness and low cost. This article deals with distinct composites and their experimental aspects having a lower thermal conductivity, summarize various key aspects highlighted by the researchers along with the techniques used. A significant variation in thermal conductivity can be observed based on the fillers of different non-degradable and biodegradable materials possessing different mechanical properties since the density of fillers plays an important role in determining thermal conductivity and mechanical properties. (C) 2019 Elsevier B.V. All rights reserved.