Twin rope technique using sub-9mm ropes involves both ropes being used as one, i.e. both ropes go through every point of protection. It is better for the rope and karabiner that each piece of protection has a separate karabiner for each rope. If twin ropes are used correctly, they have considerable advantages with regard to easier handling and higher capacity to absorb a fall. The results show that all ropes tested far exceed the UIAA standards. 10.5 mm is a fairly new diameter which has proved popular, because it is robust enough to be used as a single rope, yet light enough to be incorporated in a double rope system should the need arise.
Twin ropes are a more difficult choice, as the diameter varies from manufacturer to manufacturer.
As a general principle the larger the diameter the stronger the rope, which does leave the consumer in a bit of a quandary, as the usual reason for purchasing twin ropes is for their lightness. For example a leader falling near the end of a pitch has more usable rope, better belays can be reached on long pitches and there's more room to manoeuvre on abseils. For these reasons the climber should oonsider 50 metres. An expensive decision is whether or not to buy an 'everdry' rope. Waterproof ropes are invaluable for snow and ice climbing as standard ropes easily become saturated and heavy, more difficult to handle through belay brakes and abseil devices, and cause more friction through runners.