Axiom #1, be prepared that if you find you like rope and you get into it, your kit will be full of everything that anybody ever suggested to a beginner at one time or another. I am your support group from hell, because the answer to any question is, “you need more rope.” (It’s a meme and a fetish!)
Axiom #2, when asking yourself what kind of rope you need, there is no right answer, and there is no wrong answer. In the long run you will reach for different ropes for different applications, and each one will be a personal decision based on too many factors to simply articulate here. Refer to Axiom #1, because there will always be some application you haven’t thought of, and you will “need more rope.”
Axiom #3, the one common size that you will be able to get in almost every kind of rope from every vendor: 30′ of 6mm (1/4″). You can buy these and cut them in half to get 15′ lengths. The same size, or something pretty close to it (8m-10m lengths of 6mm), is what almost every instructional video or shibari – sorry, kinbaku – master will tell you to use. My personal take on this is that evolutionary forces have acted to tease out what works for most tops and bottoms, so you might want to go with the flow. If you don’t, you’ll end up there anyway because, “you need more rope.”
Axiom #4, I’ll badly paraphrase my friend Professor Oni, when you need a long length of rope, there is no such thing as a long enough piece. It could be a 200′ length, and it will come up 4′ short on the last turn, and you’ll have to tie in a 30′ length to finish the tie.
Corollary, when you need a little bit of rope, there is no such thing as a short enough piece. It could be a 10′ piece and you end up with 6′ left over after you’ve finished the tie.
This is why the gods invented spiral knots and wraps (coiling the rope around itself). These decorative aspects look intentional to the novice observer, but almost never were intentional on the part of the top doing the work. Once you start doing these things for decoration, “You need more rope.”
Axiom #5, There is a common conception that 8mm (5/16″) requires fewer wraps and might be more suited for larger folks. I think the larger diameter leads to more pinchiness (totally a word, I just invented it), as I find the 8mm rope more likely to roll against itself with a larger gap to roll over. Since larger folks are also usually squishy (a patented term used in the most affectionate manner, I assure you), the pinchy problem is compounded. I currently prefer the 6mm with an extra wrap or two, and a weave to keep the wraps flat. That extra wrap? “You need more rope.”
Axiom #6, 8mm rope makes REALLY BIG knots. If you’re blind and want to see the knots from space, or if you like the knot aesthetic, that’s fine. I find that my Roxy does not like to lie down on these big knots, which is somewhat limiting. It’s not a turn on to hear “ow, ow, ow, ow” in rhythm. If you already bought 5/16″ rope, (say it with me) “you need more rope.”
Axiom #7, 8mm rope is marginally stronger, however – if the strength of the rope is the only difference between falling and not falling, you’re probably an advanced rigger trying to do something with as little rope as possible, so I wouldn’t count this as a primary purchasing factor for beginners. The beginner will have many winds, and a lot of redundancy. When all else fails, apply more rope (see Axiom #1).
Axiom #8, do you have an instructor in mind? Sometimes the instructor will dictate your materials. Max is well known as preferring 8mm rope, where Monk prefers the 6mm. Max is usually dealing in suspension (a.k.a. advanced bondage). Of course, instructors will tell you, if you haven’t got their required materials because you started out differently, “you need more rope.”
Axiom #9, a length of rope more than 5 full arm lengths (your arms stretched out as far as they will go) is subject to the strong knot force. As described by Einstein during his days of tying up Marie Curie (hey, where do you think the term ‘string theory’ came from – old Albert was visualizing what happens to a length of cord when it goes into the vortex of a black hole – hint it gets longer), the strong knot force is responsible for the fact that every foot of length in a piece of rope exponentially increases the likelihood of an undoable tangle. The magic untangling device you have to get to deal with this is oddly the same device you use to create 30′ lengths in the first place – scissors.
Midori refers to the strong knot force as “kitten top” syndrome.
Corollary – extremely short lengths of rope are subject to the weak knot force. It’s the same problem, just on a different scale. All your cutoffs from dealing with undoable tangles will magically cause undoable tangles in any ropes they touch. Your best bet is to discard any piece shorter than 6 feet and see Axiom #1, “you need more rope.”
Axiom #10, Rope long enough to be subject to the strong knot force will wrap itself around your right <insert painful body part here> every time you yank on it. When it’s that long, you will yank on it at least once. Gads I’m cringing just writing this.
Confucius himself prefers to have too much rope vs. not enough, but he was aware of the strong knot force (see Axiom #9), and had plenty of wisdom for men with short ropes to help them deal. Confucious say, “man with short rope needs more rope.”
Historical side note: Vatsyayana always suggested matching the length of the lingam to the depth of the yoni, but that’s just crazy talk. All the girls like the boys with longer rope. It makes for better pictures…