The next generation of garments is sensorized, and therefore requires an adapted wireless communication tool such as a textile antenna. However, when integrating this flexible antenna into clothing, stable and reliable functioning in the operating frequency range is required. Climatic changes, especially altering relative humidity, might influence the textile antenna performance. This effect has to be taken into consideration when selecting the textile materials that comprise the antenna. A variety of antenna substrate materials has been investigated in this paper. It was found that antennas based on materials with a small moisture regain (less than 3 %) provided a more stable antenna characteristic, and can therefore preferably be applied as antenna substrate.