Textile Structure
how cloth is put together
Concept

Fibre migration — where it appears

A fibre travelling through an assembly relative to its neighbours, root-first in wool because its scales resist tip-first motion. It is the mechanism of felting, and it is rectified rather than driven, so agitation supplies the cycles and the friction ratio decides how many count.

Named by 10 essays across 5 fields — each of them below, with the objects they name alongside it.

The ratchet a wool fibre is. A fibre with its scales, and the two strokes of one cycle of agitation. The push is the same in both directions; the distance is not, because the scales resist tip-first motion more than root-first. Every cycle therefore nets a displacement in one direction, and no amount of further agitation undoes it.

The ratchet that makes wool felt

A wool fibre is covered in scales pointing one way, so it slides more easily root-first than tip-first. Agitate it and the motion is symmetric while the result is not — every cycle nets a displacement in one direction, and no amount of further agitation undoes it.

finishing · Felting Milling, on the nonwoven's own scale. Migrated fibre accumulating with agitation, measured against the stick-percolation threshold this site uses for nonwovens. Above the line the fibre network holds on its own, which is why a milled cloth can be cut without fraying — the weave is no longer the only thing keeping it together.

Milling holds the cloth a second time

This site's integrity criterion returns exactly the same answer for a melton as for the loose twill it was woven as, and it is right both times. What has changed is that a second network now holds the fabric together, made of migrated fibre rather than of thread crossings — and it is the one that decides whether a cut edge frays.

finishing · Felting What a shrink-resist treatment has to do. Net displacement per cycle of agitation as a treatment closes the gap between the two friction coefficients. The chemistry is sold as gluing the scales down; what it has to achieve is arithmetic — make the fibre slide equally well both ways and the ratchet has nothing to rectify.

Shrink-resist is one number

Machine-washable wool is sold as a coating that glues the scales down. What the treatment has to achieve is narrower and more exact — make the fibre slide equally well in both directions, and the ratchet has nothing left to rectify, whatever the friction happens to be.

finishing · Felting Z twist at 800 turns per metre. A 20 tex cotton yarn, 0.167 mm across, with its surface fibres drawn as the helices they are. The angle between a surface fibre and the yarn's axis is 22.8°, and it is the only quantity in this family: the yarn is 4.1% shorter than the fibre in it and carries 85% of the strength the same fibre would give lying straight.

Twist is one angle

Every model on this site treats a yarn as a cylinder with a diameter. It is a bundle of loose fibres, and what makes it behave like a cylinder is twist — which is a helix, so the whole subject is one angle, and the trade's twist factor turns out to be the only combination of count and turns that decides anything.

setting · Twist A 20 tex cotton yarn and the fibre standing off it. 6 mm of a 20 tex ring-spun cotton yarn with the hair population this site computes from the yarn's own count and staple — 0.89 hairs per millimetre, every one of them drawn. The two axes are at different scales and have to be — the yarn is 167 µm across and its hairs reach past a millimetre, so a picture at one scale is either a bare line or a black rectangle. Along the yarn is 99 pixels to the millimetre and off it is 74, a 1-fold exaggeration of the vertical. Lengths are drawn from the exponential the model predicts, mean 621 µm; the rules mark one, two and three millimetres with the count a hair-counting instrument reports at each, and the hairs crossing each rule in the drawing are the ones those counts are about. At the yarn's own surface the long hairs cover 1.1% of the space beside it, which is why the picture is mostly gap. Nothing here is the short population, which carries most of the protruding length and none of the reach; and a hair reaching past the room the canvas has is drawn to the edge of it, so the very longest few are shortened in the drawing and not in the arithmetic.

A yarn's surface is a distribution

This collection has computed where a cloth stops, and every one of those numbers is a statement about yarn. What a finger, a plate, a droplet or a ray of light actually meets first is a population of fibre ends standing off the yarn — and it is a population, with a count and a length, rather than a layer with a thickness.

cloth · Hair layer Where the strain goes, at a 25° twist. Extend a twisted yarn and the fibres in it are not all strained alike. If each stays at its own radius — the affine model — a fibre at helix angle θ takes cos²θ of the yarn's strain, so the fibre on the axis takes all of it and the fibre at the surface takes 82.1% of it. The core reaches its breaking extension first and the yarn cannot realise its own fibres. If instead every fibre migrates between the core and the surface, every fibre has the same mean strain and they all break together. The two are exactly computable — 0.8214 against 0.9509 of what the fibres could give — and the ratio between them, 2/(cos α(1 + cos α)) = 1.158, is what migration is worth. The shading is that arithmetic and the two panels use the same scale.

A straight fibre cannot share the load

Extend a twisted yarn and its fibres are not all strained alike: the one on the axis takes the whole of it and the one at the surface takes cos²α. So they do not break together, and what a wandering fibre is worth comes out as one expression with nothing fitted in it.

mechanics · Migration Z twist at 1600 turns per metre. A 20 tex cotton yarn, 0.167 mm across, with its surface fibres drawn as the helices they are. The angle between a surface fibre and the yarn's axis is 40.0°, and it is the only quantity in this family: the yarn is 13.8% shorter than the fibre in it and carries 59% of the strength the same fibre would give lying straight.

The other crepe is in the yarn

A crepe weave puts the texture in the matrix. A crepe yarn puts it nowhere the matrix can see: the cloth is a plain weave, and the surface comes from a thread twisted so hard that it shortens by a seventh and spends the rest of its life trying to untwist.

weaves · Texture weaves Both halves of the twist curve, at 28 mm staple. The falling curve is obliquity and is exact — the affine end of the bracket, computed from the helix and nothing else. The rising curve is cohesion and is the half this collection had declined: a fibre end is gripped by friction under the twist's own radial pressure, the fibre's strength and the yarn's load cancel out of the comparison, and what is left is a critical length that depends on the twist through a pure function of the angle. Their product has a maximum at a twist factor of 3101 — 693 turns per metre at 20 tex, a surface angle of 20° — which is inside the range spinners use. The scale of the rising curve is fitted, through a contact efficiency of 0.05, and moving it moves the optimum; what it cannot move is the ordering between two staples or two fibres, which is what the two claims made from this figure are about.

The other half of the twist curve

This collection computed the falling half of the strength–twist curve exactly and declined the rising half as being out of reach. It is not out of reach. With the grip derived rather than assumed, the optimum comes out at a twist factor — and the same twist factor at every count, which is why the trade quotes twist factors at all.

setting · Twist Compacting a spinning triangle moves one instrument and not the other. What happens to each hairiness reading when a 20 tex cotton yarn is spun compact instead of ring, as a percentage of the ring value. The total falls by 8% and the long hairs by 65%, a ratio of 8.3. The asymmetry is a prediction rather than a fit. Compaction removes ends that were unbound over a long stretch of the spinning triangle, which is the long population and nothing else; the short population is untouched, and it carries about 88% of the length the integrating instrument is adding up. So the instrument that sees everything barely moves and the one that sees only the tail collapses. The model under-states the fall in the total, because compaction certainly does something to the short population too and nothing here models it — the direction of that error is stated and it is the conservative one.

The spinning triangle decides the hair

A ring frame converges a flat ribbon of fibres to a round yarn, and for the length of that convergence the fibres at the ribbon's edges are held by nothing. Everything a spinner can do about hairiness is done in that triangle, and the two hairiness instruments respond to it by wildly different amounts.

setting · Twist Two stiffnesses, one bracket, and a ratio that does not move. The bending and torsional rigidities of a cotton yarn against its count, each drawn at both ends of its own bracket, on a logarithmic scale. The four curves are two parallel pairs: the torsional bracket is the bending bracket exactly — the fibre count over the square of the packing factor, 327 at 20 tex — so the vertical gap between the two bounds is the same for both deformations. The consequence is the useful part: the ratio C/B is 0.250 at the top of the bracket and at the bottom and everywhere between, because the polar second moment of a circle is exactly twice its flexural one.

A fabric reads its own bracket four ways

A yarn's stiffness is unknown to a factor of three hundred, and no laboratory measurement has closed it. Four unrelated everyday observations — a snarl, a knot, a flattened yarn and a cloth's own thickness — all say the same thing about which end of it a yarn sits at.

mechanics · Yarn stiffness

Named alongside it

The objects these essays reach for when they reach for this one.

Helix angleObliquityTwist factorFeltingFibre countStaple lengthBending rigidityEscape fractionFrictionHair layerHairinessIrreversibility

All concepts