Gleipnir is an etiological joke that has been taken seriously for eight hundred years.
Snorri lists the ingredients: it was made of six things — the noise a cat makes when it moves, the beard of a woman, the roots of a mountain, the sinews of a bear, the breath of a fish, and the spittle of a bird. And then the line that gives the whole passage away: though you may not have known these things before, you can now be sure there is no lie in it, since you can see that a woman has no beard, a cat's running makes no sound, and there are no roots under a mountain.
That is not a description of a magical object. It is an explanation for why six ordinary things do not exist, and the fetter is the reason: the dwarfs used them all up.
The mechanism of the story
The fetter's smoothness and softness are the point. Snorri says it was as smooth and soft as a silk ribbon, and Ásgarðr's problem is that Fenrir can see it.
The wolf has broken two ordinary chains in front of an audience, which was the gods' plan — each break made him more confident. When they produce something that looks like a hair-band, he refuses on grounds any negotiator would recognise: there is no fame in tearing a thread, and if it is made with craft and guile then it is not going on his legs. He accepts only against a pledge, and Týr gives the hand.
The narrative logic is exact. The binding works because it does not look like a binding, and Fenrir is caught precisely because he is intelligent enough to be suspicious and still agrees to a deal with a security he knows will not be honoured.
Where it was made, and by whom
Odin sends Skírnir — Freyr's servant, the messenger of Skírnismál — down to Svartálfaheimr to commission it from dwarfs. Snorri calls them the black elves and the dark elves interchangeably, one of several places where his categories of álfar and dvergar refuse to separate cleanly.
The name Gleipnir is usually connected to a verb meaning to snap or gulp, or to one meaning to slip, giving "the gripper" or "the entangler." Neither derivation is secure.
Once bound, the cord is drawn through a stone slab called Gjöll — the same name as the river at the gate of Hel's realm, which is either meaningful or a coincidence of a word meaning "the screaming one" — and driven into the earth, then fixed with a rock called Þvíti.
Six impossible things, and the folklore of them
The list is doing a recognisable kind of work, and comparable formulas turn up elsewhere in folk tradition: things made of the sound of footsteps, the breath of fish, women's beards. Impossible-object catalogues are a widespread narrative device, generally used either for riddles or for the ingredients of magic.
What is unusual here is the direction of explanation. Snorri does not say the dwarfs found six impossible things; he says the six things were once available and are not any more, because they went into the fetter. The mythology is offering a reason for observable absences in the ordinary world — a form of storytelling far more common in folktale than in the high mythological register of the Eddas.
The list also cannot be checked against anything older. Gleipnir appears in no Eddic poem; the Völuspá and Lokasenna material knows the wolf is bound but does not name or describe the fetter. This is Snorri alone.
What it means that it holds
Norse mythology's central threat is restrained by a piece of cord that is soft to the touch and made of things that are not there. That is not a failure of imagination — it is a statement about what actually restrains dangerous things.
The wolf cannot be beaten by force; two demonstrably stronger fetters failed. He is held by a combination of craft, deception and a broken oath, and it costs the god of oaths his sword-hand. Norse myth is consistently clearer than most about the fact that order is maintained by methods its own participants know to be dishonourable, and Gleipnir is the neatest single image of that.
It also does not last. The refrain of Völuspá is that the fetter will break and the ravener run free, and Snorri's account ends with the wolf lying there until Ragnarök, when he gets loose.
The ingredient list as a party piece
Gleipnir shows up in games and fiction regularly, usually as a magical chain, and the ingredient list is one of the most quoted passages in the Prose Edda — it circulates widely as a standalone curiosity, often without the punchline about why cats make no noise.
For the wolf, see Fenrir; for the god who paid for the binding, Týr; for the objects the dwarfs made in a different commission, Mjölnir and Draupnir; and for the Norse overview.
Are there other bindings like this in Norse myth?
Binding is one of the recurring solutions, and it is always temporary. Loki is bound with his son's entrails, which turn to iron. Garmr is fastened before Gnipahellir. The wolf is bound twice with iron and once with the fetter. In every case the restraint is explicitly stated to fail at the end of the world, which makes binding the characteristic Norse response to an insoluble problem: it does not remove the threat, it schedules it. Compare a mythology that kills its monsters outright and the difference in outlook is considerable.
Why does Fenrir insist on a hostage rather than refusing outright?
Because the gods have framed the whole thing as a public test of strength, and refusing would cost him the reputation the first two breaks earned him. He says as much: if he cannot get free he will win no glory, and if it is made with guile he would rather they left him alone. The pledge is his attempt to have it both ways — accept the challenge, keep the audience, and insure himself against fraud. It fails, and the sources are clear that everyone present knew it would, which is why nobody but Týr would put out a hand.