ROPE DIAMETERS

When picking rope diameters, it very relative to what you going to do with the rope! Generally the larger the Diameter of the rope, the larger area the pressure is spread over on the surface of the skin, but at the same time the harder its is to tie knots and the larger knots will be. Also the smaller the rope, the more a single width can cut into the skin (a piece of thread will cut in alot more then a piece of rope). Traditional size used in Jpanese is 1/4", but japanese tened to be alot smaller then westerns, so for beginners I suggest to start with 5/16" - 3/8" ( 8 - 9 mm) and then go up or down from there depending on what your doing with your victim for general bondage. .

On the same note, smaller sizes of rope, 1/4" or under, and twine work best for hair bondage and digital bondage (fingers, toes, nipples, penise etc).

ROPE LENGTS

What is the right lengths of rope? Whatever works for you and what you are doing!
Anywhere from 3ft to 100ft can work. Just remember the longer the rope, the longer it talks to pull rope through knots. Do not waste time tring to make and organize tons of different sizes.
Generall i believe it best to just keep a short set and a long set of rope. Short set i suggest between 6-10ft and a long set about 40-50ft tend to be good sizes. I personally use sized of 10ft and 38ft (dont ask, just workes for me). Traditional Japanese tend to use lengths of 7 meters (about 25ft). And having rope that is too long, you can always use to do something else with, and rope the too short, you can always weave another piece of rope into it to make it longer.

Strength

Rope of different materials, have different amount of weight they can handle. The breaking strain of top quality nylon twist can be defined as 5D²/300 tonnes where D=diameter in millimeters and the safe working load would be defined as S/6 where S=breaking strain. Top quality nylon braid would be S=6D²/300 tonnes. It is important to note that these formulae are for top quality nylon line. I like the Lehigh company, but their packaged nylon line doesn't live up to these standards.

A word here on breaking strain: just how important is it? I really don't know since I've never broken a rope in shibari. However, one should be aware that a struggling suspended subbie could exert a momentary dynamic load on her ropes equal to up to ten times her weight. Obviously, it would be foolish to try to suspend someone weighing 135 lb. using string with a breaking strain of 20 lb., so, if you know the numbers, never use a line with a safe working load less than the weight of your subbie.

Check out the Rope Comparison Chart for more info.