The Carolyn Pajama pattern is designed for woven fabrics but I think it could totally work with knits. I haven't had time to whip a pair up (hoping to do that in the next month or so), but in the meantime I thought I'd share a little info on piping knit fabrics for those of you renegades who are planning on making your Carolyns in stretch fabric. If you go that route, be mindful of sizing. Because the top is supposed to be loose fitting, you can probably cut in your size. The pants should probably fit a little closer to the body so I would suggest going down a size or two. If anyone makes this up please let me know how it goes!
There is markedly little information online or in any of my books about piping knits. Crafting a Rainbow has used elastic for piping, but I wanted to experiment with using a knit fabric. I mocked up a Carolyn collar with a drapey lightweight cotton lycra in two colours to see how it worked. In this example I'm using flat folded piping, but you could also experiment with adding a cord.
If you want the exposed piping to be 1/8", you'll want to cut parallel strips from selvedge to selvedge, approximately 1 1/2" wide. Most knit fabric is 56-60" wide, more than enough to pipe even the longest details in this pattern. You'll interface everything as indicated in the instructions, but please use an interfacing designed for stretch fabrics. Using the same technique I showed you for piping woven fabric on Monday, you'll want to line up your seams with your sewing plate, being careful as you sew around the curves. Normally, we use a zig zag stitch when sewing knits. However, these seams need to be stable, and zig-zagging around tight curves is tricky, so I think using a straight stitch is fine. As long as you're not tugging or aggressively pulling on the fabric I don't think you'll have to worry about popping stitches.
Try not to stretch the flat piping as you sew. Around tight corners, keep your needle down and raise your pressure foot as you turn slowly, dropping the foot after you've shaped the piping.
Notch your corners around the curves to get the piping to lay flat.
After you sew your second piece on top, you will have to aggressively grade the seams since it will be quite thick. The finished product looks quite nice though! I'm super curious to see how this looks in a finished garment.
Hope that helps anyone wanting to experiment with knit fabric!