Prusik knot

The prusik is essentially a cow hitch with several passes. The loop lies in wraps around the main rope, and both sides of the loop come out in the middle. When the loop is pulled, the wraps tighten, press on the rope and create friction. When the pull stops, they relax and the knot becomes movable again.

Because the loop comes out of the middle of the knot, the prusik grips in both directions – whether it is pulled up or down. How well it grips depends on many things: the diameter ratio between cord and rope, the material, wetness, ice or dirt, and the number of wraps. More wraps mean more friction, but also that it is harder to slide.

A neatly tied prusik has wraps that lie parallel and tidy side by side without crossing. You see the same number of wraps on both sides, and the emerging loop sits in the centre between them. Three passes in total are common. Crossed or twisted wraps grip unevenly and can make the knot unpredictable.

“Setting” a prusik means: push the wraps neatly into place and then load it as a test. Check two things: under load it must grip without slipping. Without load it must slide. The loop itself is usually closed with a double fisherman's bend; its tails must be long enough and it must be correctly tied.

The most important mistake is cord that is too thick. If it is as thick as or thicker than the main rope, it cannot bed down tightly enough and slips. Too few wraps for slick or wet rope also cause slipping. Crossed wraps are a third classic.

When a friction hitch slips under load, friction creates heat. Synthetic fibres can melt and be damaged. Another problem is the opposite: after heavy loading, a prusik sometimes sits so tight that it can barely be slid. To move it, it is best to push gently on the knot itself, without squeezing the wraps and without pulling on the loop – otherwise it grips exactly when you do not want it to.

In camp the prusik is a handy everyday helper: two prusik loops on a tarp ridgeline give you sliding attachment points to which you tie the tarp and then position it exactly where you want it. It is also useful for adjustable tie-out points on a taut line.

This page teaches you nothing about self-belay for climbing, abseiling or rescue – there, everything depends on the right equipment, the right system and practised routines. Life-safety use only after proper training with certified equipment. On icy, wet or very slick ropes it is not reliable without testing first.

The knot is named after the Austrian mountaineer Karl Prusik, who popularised it in the first half of the 20th century. Since then it has been a basic component of rope technique in mountaineering and is taught there in courses. There are many related friction hitches, such as the klemheist, which grips in one direction only.

Test with exactly the materials you are using before every use. A loop that grips well on your dry rope can behave quite differently on a wet or different rope. And check the loop regularly for abrasion or shiny, glazed spots – then it needs replacing.