Antennas made out of textile materials suffer from performance perturbing effects whose impact mainly depend on the mechanical properties of the fabrics. The soft and flexible nature of the fabrics is essential for user comfort in wearable systems, but makes the antenna performance sensitive to bending, stretching, compression, and the manufacturing process. Furthermore, water absorption into the woven textile structures can increase both the permittivity and the dielectric loss of the substrate materials. The potential performance reduction due to the material characteristics is addressed in this paper, and methods to improve performance robustness are introduced. Tests show that the use of a textile cover provides a rugged design which is insensitive to the effects of abrasion, saline water and varying climatic conditions. A dual frequency textile antenna is thoroughly tested and shown to be fully compliant with Iridium and GPS specifications.