from what I've read, yes, chlorine will break down the PUL over time. So, you should prob just designate ONE cover as your swim diaper. I'm going to do that w/one of our Fuzzi Bunz, I hear they work really well as "swim dipes"

 

I would say yes it will breakdown your PUL. One designated cover, or purchase a simple diaper or two for pool use that you have not invested $$$ into and stick to those for the pool.