Cotton, rayon, and acetate yarns were exposed for different periods of time to thermal neutrons and to gamma rays. The results have shown that total dose is the deciding factor in the extent of change in physical properties of the materials and that gamma rays (Co60) alone have essentially the same effect as thermal neutrons when the energies from the two are equated. The decreasing order of stability of the materials was acetate, rayon, and cotton. The data suggest that there are linkages in the native cellulose molecule susceptible to radiation that are not present in the regenerated materials.