Building a Rope Kit [Level 0]
Notes and Resources:
Almost any size rope can be used for bondage with enough creativity and care; however for the techniques covered in the Core Rope Curriculum, you generally want a diameter between 3/16" and 3/8" (5-8mm). The right diameter depends on the material of your rope and your style of tying more than on the size of your bottom, although wider rope can sometimes be more convenient for tying larger bodies. A good starting point for beginners is almost always 1/4" (6mm), and that's the most popular diameter in general.
Some ropes have an outer braided sheath around a core of straight fiber; most rope made for climbing is of this type of construction (sometimes called "kernmantle"). Clothesline and other cheap hardware-store ropes frequently also have a core, sometimes of a different material than the sheath. In general, any rope with a core is bad for bondage; it is difficult to handle and produces bulky knots.
Rope for bondage should be either twisted (most commonly with 3, but sometimes 4, strands), or a solid braid with no core.
When you are first starting out, it is best to avoid black rope or other very dark colors; it is harder to see what is going on with dark rope, both for you and for your teacher if you are taking classes.
It's sometimes joked that bondage ropes come in only two sizes-- too long, and too short. I recommend keeping some of each handy.
The main consideration in choosing the length of your ropes is how long a rope you can comfortably handle without it becoming unwieldy when you're pulling it through. This depends mostly on your arm span, and in part on your style of tying. I'm 5'9" and find anything longer than 27' to start becoming awkward for me.
My recommendation is to compose your kit primarily of the longest length that is comfortable for you to work with, and then add in a few shorter ones for when you just need a bit of extra to finish up a tie. The most common lengths offered by suppliers of finished bondage rope are 25', 8m (26'), and 30'. My approach to building a kit from retail bondage rope is to buy 10 of the length they offer closest to my ideal (usually 8m), take one of them and cut it in half, and another cut about 1/4 way down. That gives me a kit of 8x full length, 1x 3/4 length, 2x 1/2 length, and 1x 1/4 length. For a smaller kit, just decrease the number of full-length ropes.
When you are just starting out, or if you are doing mostly bedroom bondage, a smaller kit with a higher proportion of short ropes may be more convenient; I find in the bedroom I rarely use more than 4 ropes, and use each of full, 3/4, and 1/2 length ropes with about equal frequency.
Cutting a couple of ropes to make yourself shorter lengths is a good opportunity to test that your safety cutters work well on the rope you're using. You'll need to learn a method for finishing the rope ends; this is the one I prefer. I usually order rope with unfinished ends or simple overhand end knots, and whip all my ropes with the same twine, which makes them easily recognizable as mine. Some people like to color-code their whippings to indicate the length of the rope.
Avoid having anything hard or sharp (such as metal, or melted plastic) at the ends of your rope; if you tie enough, eventually you are going to whip someone in the eye with a rope end (quite possibly yourself). Being hit in the eye with rope is always unpleasant, but you don't want rope ends that could actually cause injury to the eye.
There is another article dedicated to rope materials. If you are just starting out and don't know what you like yet, I recommend looking for inexpensive but high-quality 3-strand cotton or nylon.