an interesting concept from guideline- this cone was designed to create "turbulence" behind it so you can tie with softer materials (i.e. marabou and ostrich) and not worry about "collapse" in the water.
thanks- this one in particular is a layering of guinea, peacock, schlappen, two shades of marabou (grey/orange) spun behind the ostrich. with these types of flies, i'm a big fan of whatever can keep the profile up and create as much movement as possible. the cone is made of brass.