The knitting industry contributes very much to the progress of the textile industries because of its diversity in production, its affordable cost, and its ease of operation, in addition to its popularity among consumers thanks to its advantages; the most important are comfort, elasticity, aesthetic appearance, and thermal insulation. The composition of the three-dimensional weft jacquard knitted fabrics affects the thermal insulation property and achieves thermal balance for the body, thus providing thermal comfort. This research aims at finding consistent standards that clarify the effect of the firmness of the three-dimensional double-weft knitted fabrics used in women's outerwear on the thermal insulation property.

In this research, five designs with a double structural composition were produced, differing in double areas and firmness areas. The produced samples were treated by heat treatment, and some of the performance properties of the produced samples were measured. The research reached these results: There is a direct relationship between the double design area, the firmness area, and the thermal insulation property, so a direct relationship between the heat treatment time and the thermal insulation property, and a direct relationship between the thickness and the thermal insulation property of the three-dimensional double weft jacquard fabrics.