Alpine butterfly loop

The loop is formed from a bight in the middle of the rope that wraps around a crossing of the two strands. This makes the knot symmetrical: pull on the loop and pull on the two strands are shared evenly by the knot. It can therefore be loaded in three directions – through the loop and along each of the two strands.

Because the forces are shared this way, the butterfly jams comparatively little and is usually easy to untie after loading. In the finished knot the loop stands roughly across the rope – exactly right when a taut line is pulled sideways. A figure-eight loop, which is meant for pull along the rope, would be less suitable there.

Another use: if the loop is placed so that a damaged section of rope lies within it, that section is not loaded when the two strands are pulled. This is a stopgap for non-critical uses and does not replace replacing the rope.

The step sequence for this knot has not yet been checked by an expert in the atlas. So always compare your knot with a reliable illustration or have an experienced person look at it. A correctly tied butterfly shows a compact, symmetrical knot body from which the two strands leave in opposite directions, with the loop standing roughly across them.

The decisive test is the function test: after setting, pull hard on the two strands in opposite directions. The loop must not change size. If it gets smaller or the knot slips, it is mistied – typically the bight went through the wrong opening, or it was twisted once instead of twice. Then untie it and tie it again.

Dress the knot before setting it and pull the loop and both strands evenly. A knot set lopsidedly can deform unevenly under load.

In camp the butterfly is the knot of choice when a line needs a loop in its middle that will be pulled sideways: a clip-in point on a ridgeline, a loop for a trucker's hitch that does not jam, or isolating a damaged section for non-critical uses.

At the rope end it is needlessly complicated – a figure-eight loop or bowline is simpler there. And it is harder to learn than the figure-eight loop; mistakes are not always easy for beginners to spot. So only use it for something important once you can tie it reliably, function test included.

The alpine butterfly comes from mountaineering and is taught there for specific rope techniques. This page is not a guide to climbing or rescue technique. Life-safety use only after proper training by qualified instructors, with certified equipment and with a check by a second trained person.

In everyday camp use: a mistied butterfly can turn into a slipping noose under load – so do the function test every time. A damaged section that has been isolated remains damaged; such rope no longer belongs in load-bearing places and should be replaced.

Practise with a soft rope fixed somewhere at both ends, such as between two chair legs. Take a bight in the middle, twist it twice in the same direction so two openings form, then follow the instructions in the entry step by step. Do the function test after every attempt. There is also a fast method that wraps the rope around the hand – it is hard to learn from a description and best practised under guidance.

In the past the butterfly was used in mountaineering to tie several people into the middle of a rope; hence the German name 'Mittelmannknoten' ('middle-man knot'). In English it is also called the 'lineman's loop'. Today it is valued above all because it can be loaded in three directions.