How To Break In A T-Shirt Combine one cup of salt with ¼ cup washing soda. Together these will work to break down the fibers of the shirt and reduce stiffness. Put the shirt in the wash – to save on water, include the shirt in other loads of items that you want to soften in the same way (other t-shirts, towels, sheets, etc.). Run the wash on high heat, and add the salt/washing soda mixture when the water is almost finished filling the machine. Then, dry on high heat. Repeat 3-5 times.