A necktie looks like a folded strip of silk and is nothing of the sort. Its behavior at the knot and its ability to recover overnight both come from internal construction.
The silk is cut on the bias
Tie fabric is cut at an angle across the weave rather than along it, which changes the mechanical properties of the cloth completely.
A bias cut lets the fabric stretch and recover diagonally, so the tie can conform around a knot and then return toward its original dimensions when untied.
Cutting on the bias consumes considerably more cloth than cutting straight, and it is the first economy abandoned in cheap ties, which then twist and refuse to hang straight.
The interlining determines the knot
Inside the silk sits a separate wool or wool-blend interlining, and its weight and thickness govern how large and how firm the finished knot will be.
A heavier interlining produces a fuller knot and a tie that resists creasing, while a lighter one gives a smaller knot and more visible texture from the outer cloth.
This is why two ties in identical silk can knot completely differently, and why the felt-like strip pulled from a damaged tie surprises people who expected padding.
One stitch runs the whole length
The folded silk is closed along the back with a single slip stitch running from tip to tip, deliberately left loose rather than pulled tight.
That slack allows the tie to elongate under the tension of knotting and to draw back afterward, functioning as a mechanical reserve.
A small loop of thread at one end, sometimes called the bar tack loop, exists to absorb that movement, and a tie that has lost it tends to pucker permanently.
Three panels rather than one
Most ties are assembled from three separate pieces of silk joined by diagonal seams, because a single bias-cut length long enough would waste an impractical amount of cloth.
The seams are placed where they fall behind the knot or under the collar, so they are structural rather than visible in wear.
Ties advertised as constructed from fewer panels use more cloth and are marketed accordingly, though the practical difference in how the tie behaves is modest.
Why hanging matters
Rolling or hanging a tie after wear lets the bias-cut silk and the loose stitch pull the fabric back toward its resting length.
Leaving it knotted holds the deformation in place, and the interlining eventually takes a permanent set that no amount of hanging reverses.
Pressing a tie flat is worse than leaving the wrinkles, since heat and pressure flatten the rolled edges that give the tie its dimension in the first place.