Commercially tapered leaders are one type of monofilament they are continueus with no knots. They are thicker at the butt line than at the tippet. A tapered fly fishing leader can be mimicked with a hand tied leader.
The butt of leader is always stiffer than the tip of the leader. The design of the leader makes it so that the leader unrolls and the fly lands gently into the water so the fly does not scare the fish. http://www.glaciertoyellowstone.com/basics/step3.cfm, this is a good link for leader construction,i make my own leaders,not only is it cheaper ,but i can make them on the spot for different situations if need be.
i do soak my leader material in warm water before i make them up,i find this soaking makes the leader material more supple and allows the knots to set better.
I fish some areas where there are lots of weeds and moss.... a knotless leader makes fishing these areas much easier... in fact it's the only way to go in those circumstances.
Tight Lines
Rob