Textile Structure
how cloth is put together
Concept

Residual twist — where it appears

What is left of a single's own twist inside a folded yarn: the twist it was spun at, less the folding twist. A single held at its ends turns once about its own axis for every turn of the fold, so the subtraction is geometry rather than a model.

Named by 2 essays across 2 fields — each of them below, with the objects they name alongside it.

Folding, and what it takes out of the singles. Two 20 tex singles spun at 800 turns per metre and folded the other way at 540 — a ratio of 0.675, which is the trade's own and is a measurement rather than a derivation. A single held at its ends and wound round its neighbour turns about its own axis once for every turn of the fold, so it is left with 260 turns per metre of its own: its surface fibres lie at 7.8° to its axis rather than the 22.8° they were spun at. Folding untwists. The short strokes are drawn at that residual angle; the two long curves are centre lines and are not the yarn — each strand is itself a bundle of 118 fibres, and the residual angle is what holds them.

Folding is untwisting

Wind two singles round each other and each one turns about its own axis once per turn of the fold. So a folded yarn's singles are not the singles that went into it, and at a folding ratio of exactly one half the two helices cancel.

setting · Ply What the folding twist costs, which is almost nothing. Folding takes twist out of the singles, which loosens their grip on their own fibres, and puts a helix round the outside, which presses on them. The two nearly cancel. The lower curve is the singles' own contribution and it collapses as the folding twist rises; the upper is the pressure the fold supplies, in the same units; their product — the yarn's realisation — runs from 0.770 to 0.696 across the whole range, a spread of 7%. The shaded band is the folding ratio the trade uses, which is chosen for torque balance and not for strength. That the two questions can be separated is the result: a spinner is free to fold for balance precisely because strength barely notices.

The singles inside a ply are not the singles

Folding leaves each single with a fraction of its own twist, which should ruin its grip on its own fibres. It does not, because the ply's helix presses on the singles exactly as a single's helix presses on its fibres — and across the whole practical range the two very nearly cancel.

mechanics · Ply

Named alongside it

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

Folding twistHelix anglePlyContact efficiencyCritical lengthFrictionObliquityPacking factorTwist directionTwist factorYarn diameter

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