Hi, I was wondering if you could possibly help me with a costume problem? If not that's fine! C: It's related to dyeing polyester at 65% and cotton at 35%.

Sure 🙂 iDye Poly works incredibly well on Polyester, however it doesn’t work on cotton. Idye (regular) works really well on cotton but not on polyester, so it’s going to be a bit of a risk to try. I just yesterday.. the day before… recently dug out some netting I dyed with iDye poly so I can show you what it can do 🙂 Photos and possibly video depending on how easy it is to focus on this netting 🙂
I’m a big fan of the stuff, though most of my dyeing has been with Dylon before they changed.