From http://www.bdsm-chicago.com/cram:
Rope Materials
Types of Rope
Cordage: rope, twine, or thread has always been an essential part of man’s tool kit These have been made of both animal and plant fibers, and now, synthetic fibers and wire are used as well. Examples of animal fiber cordage would include sinew for sewing, the Mexican braided rawhide reata, and the twisted horsehair hackamore. Probably every long-fiber plant known to man has been used at some time or other in history to make cordage. To judge the significance of rope, it should be noted that the maritime economies of Europe would never have come into existence without it and the New World would, in all likelihood, would never have been discovered and settled by Europeans. Without rope, the pyramids might never have been built, mountains may never have been climbed and there would be no shibari.
Different Ropes for Different Folks
Here, I will discuss the various types and and give my opinions of them. Owing to human diversity, I don’t expect everyone to agree with me or my reasoning. Hey, what makes the world go round anyway?
Rope for Shibari can be classed as either natural fiber or synthetic fiber and is further divided as being made by twisting or by braiding. Braided rope is made by braiding fine yarns of fibers over a core. The core can be of the same material as the shell or can be completely different, for example, nylon is often braided over a cotton core. Twisted rope is made by spinning fibers into yarn, usually with a right-hand twist. Multiple yarns, usually three, are then twisted or set into strands using a left hand twist. Multiple strands, usually three again, are then twisted or laid into rope using a right hand twist again. The twists in opposing directions create torque which is what holds the rope together. To determine the handedness of the twist, hold the rope in a line away from your body. If the twists or spirals of the rope recede to the right, you are looking at a right-hand or Z twist, if they recede to the left, you are looking at a left-hand or S twist. The latter is less common, by far, than the former and to my eye, simply looks “wrong.” Twisted rope is preferable for shibari in a couple of ways: most knots are designed so that the natural friction of the twists working against each other helps in their setting and stability. Twisted rope also leaves beautiful ligature marks on a subbie’s skin after the bindings have been removed–a lovely reminder of a happy time.
Synthetic Fibers
I don’t like them! let’s get that out of the way first. I don’t like them for Shibari, at least. The main synthetic fibers would be polypropylene, that nasty hard stuff that floats and is used for things like water-ski tow ropes: nylon; rayon; and the weird compounds used for climbing rope. Synthetic ropes have, as a class, certain advantages as well as disadvantages. On the positive side, they are very stable. They tend to be waterproof and will wash 
well. On the negative side, the can produce significant rope-burn very easily when moved quickly over the skin.
MFP ( Muti - Filament Polypropylene ), don’t confuse this with other types of rope that are not suitable for Shibari use! I personally use this type of rope for most of my Shibari work. It’s easy to keep clean, and comes in dozen of colors if you order from rainbowrope.com
Climbing rope, always braided, can be made out of several different materials, including kevlar.
Rayon can be twisted or braided and is usually used for sailing as halyards and sheets. It is very stable, has a nice texture and is very expensive.
Nylon can be twisted or braided and is very stretchy. The most commonly available types, what you would find packaged in the hardware store, are not nearly as strong as one might expect. Nylon is very slippery and doesn’t always hold knots well. In humid weather, it seems to have a moist feel to it, making it rather distasteful to me. Braided line uses a core which is not always of the same material as the surface braid. When the materials are incomparable, washing or exposure to water or humidity can and will substantially alter the characteristics of the rope.
Natural Fibers
I prefer natural fibers, well, some natural fibers. Some of them are truly nasty and are totally inappropriate for bondage. Stability varies greatly between the fibers and, of those suitable for bondage, their resistance to moisture is such that I regard them as un-washable
A word here on washability: I don’t advocate washing rope and feel that caution and personal hygiene are the answers to the problem. According to Jay Wiseman (Jay Wiseman’s Erotic Bondage Handbook, Greenery Press, Emeryville, CA; 2000, p 116) there are no known cases of anything being transmitted to anyone through rope. True, I don’t do a lot of casual play any more and, even in light of the “harshness” of the rope I use, I’ve never had an instance where I’ve caused skin to break even slightly, so for me, it’s never really been an issue.
Manila
Manila is made from the leaf stems of the abaca plant, a member of the banana 
family. The fibers vary in length from 4 to 15 feet.and are classified as hard. This is very stable and strong rope. S=2D²/300 tonnes for new, top quality rope. Typically, manilla is treated with petrochemicals to inhibit mildew and has a smell like diesel fuel. This rope is totally unsuitable for bondage, the chief disadvantage is the possibility of infection from fiber splinters that break off and become embedded in the skin.
Sisal
Sisal is made from either of two fibers from tropical plants, cesarean and henequen. These fibers are shorter than manila but have the same drawbacks and are classified as hard. If the breaking strain of Manila is given as 100, sisalana=80 and henequen=65. Again, unsuitable for bondage.
Coir
Mentioned for curiosity value, coir is made from the fiber of coconut husks, is very light and floats. The rope is very rough and stretchy with a breaking strain of about 25% of manila.
Cotton
In Japan, cotton is used for static bondage (no suspension). It comes as twist or braid and is often died red, or, occasionally, other colors. Cotton has a very low strength index and is best used for decorative work. I’ve seen some lovely twist in hardware and tack stores but it’s usually too large for bondage.
The Real Shibari Nitty-gritty
This is the rope I make and use myself. From left to right: jute, raw hemp from Hungary, and sized hemp from Hungary. The sizing in the leftmost rope probably has a casein content as the twine I made it from smelled just like Elmer’s glue when I got it. The Preferred diameter is 6 to 8 mm or 1/4″.
Hemp 
Hemp is a soft fiber that grows in many parts of the world, It is very absorbent and was usually tarred for use as standing rigging in old, square-rigged ships. The strength index of hemp is 100, identical with that of manila. This is a common rope for shibari in Japan. There is little or no danger of fibers breaking off in the skin and the feel is not uncomfortable at all. Hemp will stand up to repeated wettings but it shrinks at least 10% when wet and may not expand fully unless stretched. David El, in San Francisco, finishes his hemp rope with mink oil. I use mine raw and am happy with it that way. One day, perhaps, I will try out various finishing techniques on the ropes I make.
Jute
Another soft fiber, this is my favorite rope. It is nowhere near as abrasive or uncomfortable as it looks. The fiber is from the east Indian linden plant and has a pleasant licorice smell. It is processed with small amounts of creosote which some people may find unpleasant or irritating though, in my experience irritation is exceedingly rare. I know some subbies who, after being tied a few times who can go into headspace just smelling the rope. Jute is definitely not water-friendly since wetting expands the fibers and weakens the line. I have no idea what the strength index is though it is the most commonly (as I have recently been told) used rope for bondage and suspension in Japan. The trick is to inspect the rope and make sure it’s not fraying and to replace it before that starts to happen. Old rope can be used for static bondage, of course, where strength is not critical. Knots set well in jute but remain easy to untie. I use this rope raw, with no additional finishing but James in Seattle has been doing some experiments finishing jute with paraffin. He tells me my rope creaks when he uses it.
