Effect of Structure, Color and Finish on the MIR Emission and NIR Absorption of Knitted Textiles

The influence of direct sunlight on the heat balance of single-layer dressed people is investigated within the framework of a research project. Methodically, wool, cotton and polyester yarns are knitted in series with systematically varying construction parameters. The obtained flat knitted textiles are described as fiber-based porous structures, with material characteristics like fiber or filament surfaces, or yarn and mesh pore diameter and volumes.

The transmission, reflection and absorption fractions of mid infrared radiation (MIR) and near infrared radiation (NIR) are measured with a spectrometer using small samples of the knitted textiles. The balance of low-energy MIR radiation is found slightly influenced by the textile construction. MIR radiation is absorbed in large proportions between 75 and 93% and reflected in small proportions between 6 and 14%. The balance of high-energy NIR radiation in contrast is found significantly more strongly influenced by the construction of the flat knitted fabrics, with the absorption varying between 10 and 96% and the re- flection between 4 and 67%.

A selection of the flat knitted textiles is examined as single-layer clothing with a Guarded Hotplate, whereby both the heat emission by MIR radiation and the solar heat absorption by NIR radiation are measured. The MIR heat emission varies slightly with values between 100 and 120 W m^-2. In contrast, the NIR heat absorption is far more variable with values between about 200 and 360 W m^-2 and has a significant influence on the heat balance of people. By taking NIR heat radiation balances into account, single-layer knitted clothing can be adapted more effectively to thermal conditions of heat and cold strain, which is of great practical importance in the development of functional sports, outdoor and work clothing.