Prism99

With nylon thread, everything depends on the brand and size of the thread. YLI nylon monofilament is as fine as fine hair and works well. Some of the other brands of nylon thread are more like fishing line than thread and do not work well.

There are some things to know about working with nylon thread. My YLI is on a cone. I place the cone in a mason jar, place a thread net over it, and use an "outrigger" for threading. The outrigger is a stick that goes over my machine's spool pin and has a hole in the end for the thread. Harriet Hargrave's book on invisible machine quilting has a *lot* of good information about working with nylon thread and is worth buying. I have also seen that book online (Google books?) and you might actually be able to read what you need to know for free that way.

Nylon monofilament thread stretches, so you need to reduce the upper tension on your machine. For the same reason, you need to be careful when winding the bobbin. You have to wind slowly so that the thread doesn't get stretched on the bobbin. If your machine takes metal bobbins, these tend to work better than plastic bobbins because the plastic can distort under the pressure of the nylon. In both cases, underfill the bobbin; for a plastic bobbin, I would stop at 3/4ths full.

Not all machines do well with nylon in both top and bottom, but my machine does fine with it.

You do not want to use nylon monofilament in baby quilts, as it is so fine that if it comes loose and gets wound around a finger or toe, it can cut off circulation.

I have experimented with polyester threads, as they do tolerate higher temps than nylon and are also softer and less wiry; however, I find they show more -- at least when I am doing invisible machine applique -- so I have stuck with nylon.

You wouldn't want to use nylon filament for piecing. I just tested a piece of the YLI with my iron, 10 seconds at highest cotton setting. Although it didn't melt, it did distort somewhat. However, for use in quilting it's really not a problem as a quilt is not going to be subjected to an iron on cotton setting; normal washing temps are not going to melt it. Also, I routinely press my applique pieces and have never had a problem with the nylon filament that holds the edges down.

Edit: I will add that I recently tried Invisafil for invisible machine applique. However, it shows more than the YLI. It's a really nice thread, but not as invisible as nylon monofilament.