Rayon is a high sheen sewing thread, and often used as a lower cost alternative to silk threads. It performs well in high-speed sewing machines without breaking or fraying.
Most Rayon threads are available in 40wt, though 30wt can be found without effort. A wide range of colors and shades are available, including variegated colors.
Though some brands can be, rayon threads are not generally colorfast. It is best to avoid using any bleaching agents, including those made for colors.
Stitches sewn with Rayon threads create a very smooth consistent stitch, leading to a higher quality project.
Rayon threads do deteriorate over time, so attention should be paid to how it is stored. In low humidity regions, rayon threads can be stored in the refrigerator to extend thread life for a long as possible.
In most cases, when it comes to sewing thread, you get what you pay for. Good thread will stand up to high-speed machines without breaking or shredding. Bargain bin threads are inexpensive, but of poor quality, and will cost you in time and frustration.