I use cotton thread in the bobbin when I sew with metallic thread. You will want to use a special Metalica needle to sew with the metallic thread...the eye is larger and coated with a teflon type material to keep the needle from getting to hot and breaking the thread. The shaft of the needle is also grooved to again help with the shredding problem. Depending on the heaviness of your thread will determine how large of a needle you will want...but probably a 12 or 14.