That looks like neoprene. Works fine and stays flexible a lot longer than tygon.

There are other gas fuel lines available that work. I use neoprene inside the tank and tygon on all the lines outside the tank. The neoprene is more expensive than the tygon and the only part of the system that needs to be flexible is the clunk line. The carb line and the vent line and the fill line don't need to be flexible. Thats why I use tygon for them.

You can buy or solder little barbs on your fuel lines too. Helps keep the tubing from slipping off. I mostly do that on the outside of the tank where the tygon is. It has a tendency to become stiff and lose the elasticity over time. The barbs will keep it from slipping off. In my experience, neoprene won't slip off unless you just bought tubing that was too big for the brass lines.

There's some other tubing available. Aero - something something. Somebody will know what it is.