Invisible thread is very thin monofilament thread used by magicians to make small, lightweight objects seem to levitate and animate. It is usually made from nylon which has been separated into individual strands. Some famous illusions include the Hummer Whirling Card and the Floating Bill.
Invisible thread is also used for animating objects. Stronger invisible threads can levitate heavier objects such as people and elephants.
Invisible thread is available in stripped or unstripped form.in a unstripped form the thread when bought actually a cluster of invisible threads and has to be seperated(stripped) to be used in a performance.
Invisible thread is rarely bought or used on its own since it is very thin, if the magicians arent careful it might snap or get tangled.To overcome this an ITR(invisible thread reel) is used it is a actually an invisible thread which is wound around a plastic spool and connected to an elastic hence when the thread is pulled the magician is winding the piece of elastic so when the thread is let go it will get wound back automatically.
this is a video of ITR(invisible thread reel) being used:[1]