I agree with the differences between nylon and fluorocarbon except for fluorocarbon being able to break the surface tension of water and to sink significantly faster than nylon. The fact that fluorocarbon's specific gravity is higher than nylon leads fly fishers to think that it therefore is different enough to make a difference in sink rate for fly fishing. In most cases, that is not true.The principal reasons why I don't use Nylon in the tropics where I fish are 1) it absorbs water over time,2) it deteriorates due to UV light, 3) it's not tough enough anywhere around coral,rubble and structure, 4) it stretches, 5)it floats rather than sinks.Fluorocarbon doesn't exhibit any of these qualities.No-one I know and fish with uses Nylon monofilament.Fresh water fishing is a different ball game.I'll concede that knots need to be tied properly,but isn't that the case with every line?
Fly Fish America tested nylon and fluorocarbon leader and tippet material to evaluate whether the differences were great enough for fluorocarbon to sink faster than nylon. Here is what they found.
"The actual blend of polymers used to produce “nylon” varies somewhat, but the nylon formulations used to make monofilament leaders and tippets generally have a specific gravity in the range of 1.05 to 1.10, making them just slightly heavier than water. To put those numbers in perspective, tungsten—used in high-density sink tips—has a specific gravity of 19.25."
"Fluorocarbon has a specific gravity in the range of 1.75 to 1.90. Tungsten it ain’t, but it is significantly more dense than nylon. But is it sufficiently dense to quickly and reliable break surface tension and sink all by itself, even at zero contact angles, and even in the smallest diameters? No, it’s not. Our testing reveals that most brands of fluorocarbon tippet material in 0X to 8X diameters are no better than nylon at breaking surface tension and sinking on their own."
There is another reason why both nylon and fluorocarbon tippets and leaders float. During extrusion of the leaders, both nylon fluorocarbon are coated with a lubricant that facilitates extrusion. So both nylon and fluorocarbon come precoated with a a thin coating of floatant. This shiny coating repels water and acts like a floatant.
Furthermore, the specific gravity of salt water is 2.5% higher than fresh water, so this makes sinking a tippet in salt water slightly more difficult.