After I felt this, will it still curl?
Maybe…maybe not. Some yarns felt tighter than others. A tight fabric probably will not roll…but you never know til you try.
I’m wondering, are you felting a flat piece of knitting?
I just did a little sampler of some fair isle to test for a purse I’m making, and after felting the swatch stayed flat. I am a pretty loose knitter, but I used Cascade 220, which seems to felt up pretty tightly and nicely. You might need to block the fabric out flat once it comes out of the washer to make sure that it will stay flat.
Yes, it’s a flat piece.