A couple suggestions for you.....
Be proactive in it not getting dirty in the first place, or at least slowing down the process. Wear a lightweight set of polypro long underwear underneath to protect the polartec from your sweat, etc.
Secondly, with regards to the Thinsulate DUI garments, DUI does recommend NOT using detergent as it does break down the material and reduces the fabrics ability to do what it's supposed to do. When I first got my DUI Thinsulate underwear, Dick Long told me to my face at a DOG event to not wash with soap or fabric softener and to only clean it when
absolutely necessary and to use a cup of bleach in the wash water, adding the suit to the washtub after the filling and adding the bleach.
But with the Polartec, I was told at this last DOG event I could wash with mild detergent. I would avoid fabric softener as it does mat fabric. I've had other Polartec products from LLBean and NorthFace that state specifically NO FABRIC SOFTENER.
So, long story short....be proactive, help your suit stay cleaner, longer, by wearing another garment next to your skin. And consider not using detergent for every wash, but maybe adding a cup of white vinegar to the wash water instead to drive out the smelly little gremlins that want to take up residence in your underwear.