Polyester is a breathable and stretchy fabric, which makes it great for sports and athletic wear. White polyester can make your sports gear stand out, on a team or even on the road at night, but it can also start to yellow and look dirty after many uses. Keeping white polyester sports clothes clean is easy with a few extra steps when washing them.Mix together in a bowl two parts warm water to one part baking soda. Stir and add water or baking soda as needed to make a thin, watery paste.Dip a toothbrush into the bowl to collect the paste and then gently brush the paste into any stained areas of white fabric. Dip again and apply it on the inside of the fabric as well, in order to get at stains from both sides. Repeat steps until all stained areas are covered.Allow the baking soda paste to set into the fabric for one hour. Collect the garments and begin washing them as directed with your normal detergent. Typically a warm wash is used on polyester fabrics, but mind the tag to ensure you are treating your specific garment correctly.Pour a ½ cup of distilled white vinegar into the washer when the rinse cycle begins. The vinegar will further help with stain removal, while freshening and whitening clothes. For a large load, add another ½ cup of vinegar.Dry garments as directed or allow to air dry to ensure there is minimum shrinkage. If any stains persist, repeat the previous steps a few more times.