The Difference Between Single, Half, and Twin Rope Systems

When climbing, a dynamic rope should be used. Dynamic ropes are built to have stretch so they can help absorb the impact of a fall. There are a few different types of dynamic ropes and each have their own use. We asked one of our Sales Reps and frequent climber, Evan Watts to describe the three types of dynamic ropes: single, half, and twin, and why you might need one over the other.

Single Rope

A single rope is pretty self-explanatory, and the most familiar system used in the United States. One rope is used for every process in the system, which includes clipping it into every piece of gear, tying in to both ends, and then rappelling with the rope folded in half (effectively halving your available lengths for rappels.) These ropes are generally thicker and can take more abuse than the other systems. Sometimes a tagline (a length of cord or rope not intended for dynamic loading; usually very thin and light) is used to supplement the length of the rope and allow you to rappel the whole length of your single rope. Single rope systems are used for sport climbing, some trad climbing, and some alpine climbing.

Need a rope recommendation? The Spirit Arc 8.8mm Unicore is great because it combines an ultralightweight and a thick, durable sheath. It is also a half and single rated rope.

Twin Rope

Twin rope systems employ two ropes that are thinner and stretch more when loaded, and both ropes are clipped into each piece of gear along the way. The advantages to this system allow you to split the weight of rope between two people, and you can rappel the entire length of the shortest rope when you tie them both together. Twin ropes are often (nearly always) certified to be used as half ropes as well. 

Need a rope recommendation that you can put a little more abuse into? Look no further than the Oxygen II. While twin ropes aren’t exactly the workhorse in a climber’s quiver, the Oxygen II comes with Edelweiss’ reputation for a burly sheath. If you were a Brit climber, on wandery quarry rock, you would probably have a pair of these as your go to lines.

Half Rope

Half rope systems employ two ropes as well but instead of clipping both ropes into each piece of protection together you clip the ropes separately and along different lines of travel. For example, if you are climbing back and forth between two cracks that are widely spaced apart, you would clip one rope into gear along the right crack and the other rope into gear along the left crack. This allows both ropes to maintain straighter lines, whereas clipping a single rope or twin ropes back and forth would create unwanted amounts of rope drag and friction. If you were to fall in this system the idea is that one of the ropes would take more of the force, but as it stretches to its maximum the second rope begins to take force as well, distributing the force between the two (although not often evenly). This rope system enjoys the same rappelling and weight division benefits of twin ropes.

The Performance 9.2mm Unicore is a great option for half rope systems because it is a triple rated rope.

It is important to note that ropes used in twin or half configurations often have much higher elasticity to account for the fact that the force is being displaced through two ropes instead of one. Due to some tricky physics problems that we won't go into, single rated ropes are not always stretchy enough to be used in these ways, and can actually magnify forces on gear when used improperly in twin/half configuration. There are ropes on the market that are “triple rated”, meaning they can be used as single, half, or twin ropes.