Thanks Martina. Lutrador is similar to non-woven interfacings. I'm not sure what the material is that it's made from. It comes in a variety of weights ranging from very lightweight (like interfacing) all the way up to the weight that I used for this piece which was about the thickness of card stock. Anyway, if you stitch on it with cotton thread and then use a heat gun it will start to develop holes. The holes stop wherever there is cotton thread.
I did a two step process with the stitching, I stitched on it with cotton thread using some of the decorative stitches on my regular sewing machine, then I took it over to my PQ1500 straight stitch machine and FMQ'd it using some of the Westalee templates to get the large spirograph-looking motifs (circles and flower-ish things). The cotton thread did a good job of stopping it from disappearing completely (except where I got a little heavy handed with the heat gun LOL).
That's the lacy effect you see.
Rob