Thermostable polymers and, more particularly, thermostable fibers and films are becoming more and more important as the demands of space-age technology increase. In the preparation of thermostable fibers having good tensile strengths and practical utility the processibility of the polymer is of great importance. Aromatic polyamides meet the two most important requirements: a high degree of thermal stability and an ease of preparation as viscous solutions that can be spun into fibers or cast into films.