Used to manufacture a variety of clothing, from swimsuits and tops to uniforms and coats, polyester is a versatile, strong and flexible synthetic fabric. However, one down side of white polyester is its tendency to yellow, which occurs for a variety of reasons, from perspiration stains to the minerals in your home's water. Whatever the case, it's possible to whiten your yellowed or drab polyester without damaging or weakening the fabric.
Fill a plastic bucket or basin with 1 gallon of lukewarm water. Add 1/2 cup oxygen bleach powder to the water. Stir the water with your hand or a large spoon to help dissolve and incorporate the oxygen bleach powder. Unlike traditional chlorine bleach, which can damage or degrade polyester, oxygen bleach is sodium percarbonate, which activates when combined with water to help lift the stains without causing any damage.
Submerge the polyester pants into the oxygen bleach mixture. Allow the polyester pants to soak in the oxygen bleach mixture for at least 30 minutes. If the yellowing or discoloration is severe, allow the pants to soak for 1 or 2 hours or longer.
Remove the polyester pants from the oxygen bleach powder solution and wring out any excess water. Load the polyester pants into the washing machine alone, or with other white polyester garments. Add liquid laundry soap according to the package's label and 1/2 cup oxygen bleach powder to the washer before turning the unit on. Launder the clothing on the hottest setting recommended on the polyester pant's label.
Allow the washing machine to run through all its cycles before removing the polyester pants. If you're satisfied with the results, dry the pants according to the label's directions. If not, run the pants through a second washing machine cycle on the hottest water possible, liquid laundry soap and 1/2 cup oxygen bleach powder.