In this research, we study the effect of adding cotton fibers on the acoustic and mechanical properties of clay bricks composed of clay, sand, and gypsum. We made 11 samples of these bricks and changed the percentage of cotton threads from 0% to 10%. We measure the change in the speed of sound transmission and calculate the value of mechanical stresses. The results showed that adding 3% of cotton fibers gives us the best percentage of hardness, 45.7%, and isolates 4.2% of sound. The portion of sound insulation also increases when we increase the portion of cotton fibers. These results enable us to use these bricks in the construction field to add the best performance to structures and to insulate sound inexpensively.