To restore polyester sports t shirts if they are dingy, there are a few things you can try. For 100% polyester white t shirts, they actually can be washed with Clorox(r) Regular-Bleach, and you can start with a pre soak. Add 3 Tablespoons Clorox Regular Bleach to 1 gallon cool water and stir. Add the shirts, fully submerging them, and let them soak for 5 minutes. Drain the soaking solution and then wash the t-shirts in hot water using detergent and 1/2 cup Clorox Regular-Bleach. Finally, let them air dry. This can be very effective at stripping dingy build up from an item.