The present paper describes the results of a preliminary study of certain physical and thermal properties of benzhydrylated cotton yarns. The 2Wyd. lengths of 7/2 yarn consisting of purified mercerized cellulose were reacted in a special reactor to various degrees of substitution from DS 0.31 to DS 1.22 with benzhydryl bromide in a mixture of equal volumes of 2,Glutidine and dimethylformamide. The products were examined for tensile strength a t break, which decreased only slightly with substitution; ultimate elongation, which was relatively uniform a t 6&70% of the control yarn; and tenacity, which decreased with substitution largely due to added weight. The energy of rupture remained relatively constant a t about 50% above the control. Tensile stiffness decreased progressively with substitution to about 25% of the control. Density decreased lCrll% with substitution. Crystallinity of the cellulose largely disappeared with substitutions above DS 1, and the lattice of benshydryl cellulose began to appear. Stiffness, elastic recovery and work recovery were measured on Sin. specimens of the yarn in an oven while they were subjected to repeated extension to about 1 4 % and relaxed aa the temperature was raised twice to 200ยฐC. and lowered. During the heating phase of the fist cycle the yarn underwent considerable heat adaptation. However, during the cooling phase and during both heating and cooling phases of the second cycle, the yarns showed generally favorable behavior. Attempts are made to interpret the results in terms of molecular modifications.