We've all done stuff like this. I've only used poly batting a few times, and the scraps I have left are completely different from each other. One has a very pronounced scrim, others not. I do know that it's from JoAnn's, however.
Do you have any idea if you bought it online or locally? If online, I would be going back through credit card statements to see if something rings a bell. That might narrow it down. If locally, I'd be hauling the project in there. There has to be a solution besides randomly buying things and guessing. Ugh.
Do let us know how you figure it out.
hugs,
charlotte