The terminal tackle is critical, we can spend hundreds on a fancy rod and spoil it with the wrong terminal tackle, this is where fluorocarbon materials are beneficial in the last 9 to 12 feet between our fishing line and flies. For fly fishermen the choice of terminal tackle fluorocarbon tippet material is the often the preferred in the debate nylon and fluorocarbon because vs nylon because the refractive index is close to water the materials appear almost invisible on or in the waters surface making your flies more realistic. The strength vs nylon materials is excellent however unlike nylon tippet you willl find fluorocarbon has little stretch, this means if you use a "stiff fly rod" tippet size consideration is important because as is little stretch you risk break off if you do not use an appropriate strength for the fish you are targetting. Avaliable for leaders and tippets as a tippet spool can be stored easily.
Materials having a specific gravity in excess of 1.00 are heavier than water, Fluorocarbon has a specific gravity in the range of 1.75 to 1.90 and will sink in theory hence we use fluorocarbon for droppers and just final tippet connection to dry flies. Fluorocarbon usually does not fully break the waters surface tension hence can be used for dry flies. Knot strength is critical with fluorocarbon as it actually heats while being tied. Personally we put the knot in our mouth while we tighten the know and then use a drop of superglue to ensure that the dropper is 90 degrees to the tippet and ensures added strength. As a tactic we often use tarpered leaders to help turnover and add fluorocarbon tippet to tippet for the point fly and add fluorocarbon droppers becase of the refractive index.
Some fluorocrabon tippet is fantastic and if using spey line recommendations are that use use Seagar Ace Hard as it has is highly abrasion resistant. Fluorocarbon can be used for leader or tippet. Knots used for fluorocarbon include the Improved Clinch Knot or Surgeons Knot. Fluorocarbon can be used with tippet rings if you wish easily.
We love Seaguar fluorocarbons as they are the thinnest diameter for strength of fluorocarbon lines that we have found. This is our go to leader material.