The butterfly is generally not one of the standard climbing knots beginners learn, but it’s well worth learning once you have mastered the basics.

It's often referred to as an “alpine” butterfly, but I have no idea why. Let’s drop the “alpine” and just call it a “butterfly” knot, okay?

Photo: butterfly knot used to isolate a damaged part of the rope.

How is the butterfly knot useful for climbers?

1. The butterfly is generally easier to untie after it’s been weighted.  Use it anytime you're significantly weighting a rope (like fixing ropes for a big wall, or tying off one end of rope for snow anchor testing or crevasse rescue practice.)  Grab each of the "wings" of the knot and flex them back and forth to untie. Once you gain some experience with the butterfly knot, you may find that you use it to replace the figure eight on a bight in just about every situation.

2. It’s symmetrical and can be loaded on either strand. This makes it a good choice for the middle member(s) on a rope team. While a figure eight or overhand on a bight is acceptable for the middle person, it’s designed to be weighted in only one direction. As the middle person on a rope team, you don't know which strand will hold you in a crevasse fall.

3. It’s adjustable. If, after you make the initial loop, you decide it needs to be a little longer or a little shorter, you can feed the slack through the knot to adjust the size of the loop. (You can do this with a figure 8 on a bight, but it's quite a bit more awkward.)

4. It can be tied as a “brake knot” between rope team members for glacier travel, to help minimize the length of a crevasse fall. Any kind of crevasse rescue situation is more difficult with just one person doing the pulling, but if you tie a few knots in the rope between you and your partner, these can hopefully catch on the lip of a crevasse in the event of a fall, and minimize the length of the fall. (Yes, they can complicate the rescue, but that’s another topic.) Under the right conditions, this has been tested and proven effective. There is also another knot that has a slightly larger diameter called the brake knot, which may be preferable for two person crevasse travel, but the butterfly is acceptable.

5. It can isolate a damaged part of the rope. Through stepping on the rope with a crampon, an ice tool puncture, being loaded over a sharp edge or maybe rock fall, a rope might get some minor damage so you’re not comfortable using it anymore. With the butterfly, you can isolate the damaged part of the rope inside a loop of the knot and you’re good to go, with a near full strength and full length rope. (Now you need to figure out how to pass the knot while you are on rappel or belaying . . . but that’s a different topic!)

How about a directional / in-line figure 8?

This might be a useful knot in some sorts of rigging situations, but for recreational climbing I personally don't see a need for it. Anything the directional figure 8 can do, the butterfly can also do, so why bother?

That's not just my opinion, Australian rigging expert Richard Delaney feels the same way, check out the short video below.

And, because it's pretty much impossible to explain how to tie a knot in words, here is a short and sweet video from REI that does the job.

(It's not my preferred method, because this darn knot has probably more ways to tie it than just about any other, but it works fine. My advice: just learn one good way to tie this knot and don't confuse yourself with several.)