well the thing is that it all depends on the situation, all thread can be seen it isn't really invisible.
But it can be, let me explain.
If you use Invisible thread and you float a dollar bill spectators are looking for a thread, in this situation I hope you took all the necessary precautions.
Since you are doing a floating cigarette make sure lighting is coming from behind you, it will prevent reflection, you might see it but they won't.
Also don't use white or black
White is bad because the thread is black and if the thread is staitionary you might be able to see it. using black is also bad because, black is the absence of light. If the thread caught any light it would shine bright on the black background.
But if you use gray it hides the thread perfectly.
If you cannot control your background, be the background.
Hope this helps a bit.
PS
I have used wholy nylon for 5 years for my non elastic thread and never been caught. I am assuming you are doing the Fearson Hookup for the invisible thread.