The benefit of half ropes becomes evident when your route wanders all over the cliff. A single rope will put a great deal of friction in your system, which feels like you re climbing with a Mac Truck on your harness. In contrast, half ropes allow you to stagger the ropes in your protection, reducing the amount of friction. They are also a backup in case one rope gets cut in a rock fall or by being stepped on by a crampon. Half ropes are great for ice climbing and alpine rock.
Twin ropes are similar to half ropes with one major difference.
Twin ropes must both be clipped into the same piece of protection. These aren t as popular as the other ropes but are still useful in alpine situations when you want to shave those ounces. Twin ropes are marked with an infinity symbol in the circle at the end of the rope. Length Rope lengths are measured in meters. A longer rope is heavier, but useful for climbing longer routes and running pitches together.