Thanks all!

In my opinion, rayon thread is not strong enough nor always colourfast. If it was good quality rayon, I would have a different opinion.
I think the rayon could be used for surface embroidery but not for sandwiching. Check for colourfastness as well. All the best with it.

I have a commercial embroidery machine and I often use polyester embroidery thread in my quilting. I have used it on top and in the bobbin. It has a beautiful sheen.

I use Isocord embroidery thread all the time to piece and I have never had any problem with it at all.

Serger threads aren't as weak as one might think. I've even made FSL on my embroidery machine with it, I just slow it down and use a larger needle and no breaking thread. The reason sergers use more than one thread is fist of all, there are no bobbins the wind, instead one or two of the spools go thru loopers to complete the stitch with the needle(s). All of the other spools of thread are used depending on what stitch or technique you are using. Mine does chain stitching and overlock plus lots of deroative stitching. I personally use cotton thread to quilt with especially if its a quilt that I want to last a long time because it won't cut thru the cotton fabric. I do agree, I would not use rayon thread due to the strength and also it doesn't hold up as well for washings or high heat, like ironning.

http://seamslikealot.blogspot.ca/201...many-uses.html

Lots of thread info here.

I have been using the Sulky rayon thread in FMQ. Do you guys think that's strong enough... ?It hasn't been through the test of time here, but I love how beautiful it is and how easily it sews. However I hate to think I'm doing my quilts a disservice.

Works great! I love it for quilting. Leah Day used it exclusively last time I knew.