Prism99

I have used YLI nylon monofilament thread (.003mm) in top and bobbin. Works fine. Some people think nylon melts and poly doesn't, so I used my hottest iron temperature on both. My YLI nylon monofilament did not melt or change color or become brittle; looked just the same after using a hot iron (Rowenta) on it for a couple of minutes. Some people think nylon becomes brittle over time. Maybe the old type of nylon thread did, but I don't think the YLI monofilament does. I have some older quilts that it was used on, and there has been no change in the thread.

I tested the Superior Monopoly (not reduced-sheen version, though) on some machine applique to see if I would like it better than the YLI nylon monofilament. It was not as invisible as the YLI, so I saw no reason to change. It would work fine for SID, I'm sure, but I think it ends up being more expensive than YLI. I bought a cone of the YLI many years ago and still have lots of it left. If you decide to compare, it's pretty easy to figure out cost per yard and compare prices. The reduced-sheen aspect of the Superior thread might be nice for applique where the thread is very visible around the edges, but I don't think it's necessary for SID where the stitches are more hidden in the fabric. For SID, reduced-sheen would not be a deciding factor for me.

Edit: Some people have problems using nylon monofilament top and bobbin. I think this is usually because they are not aware of how the machine needs to be set up. Nylon is stretch, so top tension needs to be reduced a lot. The bobbin needs to be wound slowly so the nylon thread doesn't get stretched as it is loaded onto the bobbin. Also, all bobbins need to be under-filled to make sure that they nylon doesn't distort the edges of the bobbin. Metal bobbins are okay with just a little under-filling. Plastic bobbins aren't as strong and should be filled only 3/4ths full.