The main goal of the presented study was to develop new multi-layered weft-knitted structure for thermal insulation and to investigate the dynamic of the heat transfer through this fabric. For knitting of outer and inner layers of this structure, different raw materials of yarns were used, i.e. wool, cotton, polyester and acrylic yarns. All the newly developed multi-layered weft-knitted fabrics show thermal insulation as, after 1 h of observation, temperature on the outer layer of all tested fabrics does not reach 40℃, i.e. the temperature of a heated plate. The results of this research showed that the nature of the yarns has a significant influence on the air permeability and dynamic of the heat exchange through the multi-layered structure, as it influences porosity of the knitted fabric. The results showed that the best fabric was the one where the outer layers are knitted from woollen yarns and the inner layer from polyester filament yarns.

The main goal of this research was to determine the influence of the inner layer thickness and tightness, which depends on the length of the float determined by the float step and number of floats in the pattern repeat, on the thermal insulation and air permeability of the multilayered weft-knitted fabric. For this reason, weft-knitted spacer fabrics were produced by using woolen yarns for the outer layers and polyester filament yarn for the inner layer, with the number of floats in the inner layer varying between two and 20. Results from this research showed that the consequent increase in thickness and tightness of the spacer fabric’s inner layer has unequal effect on the thermal insulation and air permeability. Therefore, similar thermal insulation can be achieved by having significantly higher air permeability. This is especially evident over a long period of time.