Polyester filament yarn covered with a cut metallic film at regular intervals. This high-grade metallic thread is made for embroidery, embellishment and all other decorative applications.  It runs exceptionally well with all embroidery threads on all embroidery machines.  In my personal experience, there was no breaking in 40,000 stitches when using a thread net, a size 14 needle and slowing the machine to 500 stitches per minute. I have run this metallic thread at 1300 stitches per minute - the thread broke, but it stitched quite a while before it did!