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Dynamic Ropes
In climbing usage, dynamic rope refers to those ropes which meet EN892 (and optionally also UIAA 101). Modern climbing ropes are made from nylon (aka polyamide) and are of kernmantle construction, meaning they feature an outer sheath (mantle) woven around the inner core (kern). The 'dynamic' in their name refers to the ropes ability to stretch under load, a property which dissipates the force when the rope arrests a falling climber. Dynamic Ropes fall into one of three categories;
Single Ropes
Designed to be used individually, a single rope is tested with a factor 1.77 fall on a 2 metre test section of rope with an 80kg mass. The rope must produce a force of under 12kn on the first fall and hold at least five falls in succession. Single ropes have diameters from 8.9mm through to just over 11mm, with the most common sizes being in the 10mm to 10.5mm range. All of the club ropes are single ropes in the 10-10.5mm size range.
Half Ropes
Half ropes are designated by a 1/2 logo on the end markings and are designed to be used as a pair but with each strand clipped to alternate pieces of pro. This allows you to reduce rope drag on wandering routes, reduce fall lengths during clipping, means you can abseil a full rope length and provides some redundancy. Half ropes are tested to a similar test but with a 55kg test mass and must not generate a force over 8kn. Half ropes are typically 8.0 to 9.0mm in diameter.
Twin Ropes
Twin ropes are designated by an overlapping circle logo and are designed to be used as a pair, but are treated as one, so both strands are clipped to each piece of gear. This offers benefits of redundancy and increased abseil lengths. Twins see most of their use in alpinism where their light weight and use as alone in glacier travel are an advantage. Under EN 892 twin ropes are tested as per single ropes but with two strands of rope together and they must hold a minimum of 12 factor 1.77 falls. Twin ropes have diameters down to 7.5mm!!