Our Athletic Series is a blend of yak, Tencel, and other innovative sustainable materials. Tencel is unique in that it can be used in place of other regenerated cellulose fibers such as viscose rayon as it is a high-tenacity cellulosic fiber. Tencel is comprised of pulp from trees that is dissolved into a non-toxic organic solvent. The solvent is recycled in a closed-loop process – more than 99% of the solvent is recovered and reused.