Make sure the product is suitable for polyester, as some things don't stick to it.
And there are these products from NIKWAX. On the right side of their site, use the 'Which product do I use?' resource, and two products will come up for polyester clothing.
WARNING & DISCLAIMER:
SELECT AND USE OUTDOORS AND SURVIVAL EQUIPMENT, SUPPLIES AND TECHNIQUES AT YOUR OWN RISK. Information posted
on this forum is not reviewed for accuracy and may not be reliable, use at your own risk. Please
review the full WARNING & DISCLAIMER about information on this
site.