In this research work, it is proposed to study the thermal comfort properties of socks made from virgin cotton and recycled polyester fibres and its blends. To determine the thermal comfort properties of socks the following parameters such as thermal conductivity, thermal resistance, air permeability and relative water-vapour permeability has to be investigated. Amongst the blends, higher the addition of recycled polyester content results in increased air permeability, thermal resistance and relative water-vapour permeability and decreased thermal conductivity values than the virgin cotton blends. Furthermore, it is noticed that recycled polyester ratio increases among the blends the fabric become thin, lighter and more porous with better thermal resistance, air permeability, relative water-vapour permeability and lesser thermal conductivity than the virgin cotton ratio in the blends. It is suggested that modifications in the fibre blends lead to changes in the fabric properties such as thickness which in turn affects the comfort properties of socks. The findings were statistically evaluated by analysis of variance (ANOVA) by using SPSS 15.0. Statistical result analysis also reveals that the blend ratio significantly affects all of the thermal comfort properties of the socks. © 2021, The Korean Fiber Society for Fibers and Polymers and Springer.