Set the wash cycle to normal and use a gentle laundry detergent. Because polyester is a synthetic material, high heat can break down the fibers and cause damage to your clothes. As a result, polyester should be washed using warm or cold water. Make sure to check your care label., Wash in cold (30°C or below) water, whether using a washing machine or washing by hand. Give garments a gentle stretch when they come out of the wash to get them back into shape. Always air dry: dry clothes flat and out of the sun if possible.