As far as I can see on the Penguin site you can order the i-boss reel loaded with either thread, but I don't see a package deal. I bought mine years ago from James at the source and bought al a carte. IT is IT. Kevlar sounds as if it should be stronger and it is, until it breaks. It is also more visible and shines (although a Sharpie may help). Wooly nylon is flimsy feeling and hard to see but still does the trick. If you like working this way, you'll get familiar with one of the varieties. Much of IT work (using an ITR) is not done under conditions of tension, whereas single strand anchoring may require tension. You can fool the dog right away with either thread or set up.