I don't buy rayon thread anymore and stick with poly. Besides the major facts of rayon being weaker and not color fast, it can also break like crazy in new embroidery machines that have a higher speed. Yes, you can set you machine to go super slow, but that wastes time and it takes so much less time to go full speed with poly.

I have a 9500 and use poly embroidery thread, also cotton machine quilting thread, and some cheap serger thread. I also have rayon. I can't remember the brand of the rayon, but it comes with a plastic dome over the spool. Just depends on the effect I am going trying to achieve.

I mostly use the poly embroidery thread. Robison Anton from my Janome dealer, and Coats n Clark from Walmart. Yup, the C C brand from Walmart. Haven't had any trouble with it in 2 years. I do like the Robison Anton a little better.