The knowledge of the thermal properties of textiles is important with regard to their vast applications in most industries. Thermal properties, as one of the physical features of a textile, are influenced by its structural parameters such as thickness, density, and so on. In this study, a new structural model is developed to predict the effective thermal conductivity in knitted spacer fabrics. In the first step, a spacer fabric was considered as a three-layer set. The thermal conductivity of each layer was calculated separately, and then the effective thermal conductivity of fabric was determined based on its structural parameters. The performance of the proposed model was evaluated using spacer fabrics, and the results were compared with those of other models. The results of the new model and the experimental method showed that the most effective parameters involved in thermal conductivity are thickness, porosity and density. A good agreement (with R² = 0.91) was found between the results of the proposed model and the experimental values.