The stabiliser I have is the "fabric'ey" style one, it sort of looks like interfacing. I do have the plastic type one in my sample pack, but I was left with the impression that this was more a floating use one, to go over stitching on towels.
I had another test stitch out, this time on a piece of linen blend, well prewashed. I still get the puckering, but it seems like the thread is shrinking this time, rather than the fabric. How on earth do I stop that?