The garment with strips in its seams is the one that comes back from a wash looking wrong in a way that is hard to put into words. The cloth is fine. The seams are intact. But a line that used to be smooth now has a wave in it, or something hard is standing away from a seam, or the whole front has gone slightly soft and will not sit straight. What has happened is not to the fabric. It is to the thin strips hidden inside the seams, which were doing structural work and have stopped doing it properly.
What boning is there to do
A structured bodice is a garment that has to hold a shape with nothing underneath to hold it there. Cloth on its own cannot manage that. A woven fabric under tension pulls toward a straight line between its anchor points, and the more it is tensioned the more it tries to flatten, pucker and fold along its seams.
Boning resists that. It is a flexible strip, stiff in one direction and bendable in the other, run along a seam inside a channel so that the seam cannot collapse or buckle. The strip takes the compression the cloth would otherwise have to take, and the seam line stays where the pattern put it.
The strips were whalebone historically, then steel, and for most of the last fifty years plastic. Modern plastic boning is usually polyester or nylon, extruded as a flat strip, sometimes supplied with a woven casing already around it and sometimes bare. Spiral steel is still used in better made garments and behaves differently in every way that matters here.
The point of all of it is mechanical. A strip of boning is a structural member inside a soft structure, and like any structural member it only works while it keeps its own shape. A strip that has gone wavy is no longer holding a line. It is just something stiff inside a seam, and the seam goes back to doing what cloth does.
The channel and the strip inside it
The strip does not float free. It sits in a channel, which is either a separate tube of cotton or twill tape stitched to the seam allowance, or the seam allowance itself folded over and stitched down to form a tunnel. The ends are closed off or tipped so that the strip cannot work its way out under load.
That channel is almost always a different material from the strip, and frequently a different material from the face fabric as well. So a single seam can contain three materials with three different responses to water and to heat, all stitched into one line and expected to stay the same length as each other for years.
A well made channel is only slightly wider than the strip, and that is deliberate. Too tight and the strip cannot flex at all. Too loose and it rattles about, twists on its long axis and ends up sitting on edge, which is the first thing to check if a seam has suddenly developed a hard narrow ridge along it.
Length matters as much as width. The strip is cut a little shorter than the channel so it has somewhere to go when the garment flexes. If the channel shortens and the strip does not, that clearance disappears, and the strip has nowhere left to go except out of line.
Heat and permanent set
Plastics of this kind are thermoplastic, which means heat softens them and cooling hardens them again in whatever shape they happened to be in while soft. They do not have a single melting point so much as a range over which they go from rigid to rubbery. Well below that range nothing happens at all. Inside it, the strip remembers.
A tumble dryer on a hot setting sits uncomfortably close to that range for the lighter grades of strip. Nothing melts and nothing looks dramatic while it is happening. What happens is that the strip goes slightly soft while being folded, pressed and bent inside a tumbling garment, and then cools again in the bent position.
That is a permanent set. The strip is now straight in some places and curved in others, and it is exactly as stiff in its new shape as it was in its old one. Flexing it by hand achieves nothing useful, because you are not softening it again. You are bending a strip that will spring straight back to the shape it was set in.
An iron does the same thing faster and more locally. Pressing over a channel puts heat directly into the strip underneath, and a strip that softens under an iron takes the exact shape of the pressure applied to it, including the shape of the iron’s edge. That shows up afterward as a flat spot or a kink in an otherwise smooth line.
Why the channel shrinks and the strip does not
Cotton twill tape, which is what a great many channels are made from, shrinks in water. It shrinks the first time and a little more after that, and a tape that gives up even a small percentage of its length across the span of a long seam has moved a distance you can see.
Plastic does not shrink in water at all. It does not absorb water, so it does not swell and it does not relax, and the strip that came out of the wash is exactly the length it was before it went in. The channel around it is now shorter than it was. The strip has not changed by any amount.
Something has to give. Either the channel puckers along its length, gathering the fabric into small ripples between the stitches, or the strip pushes against the closed end and works its way toward the surface. That is where the familiar complaint comes from: a hard end standing proud of a seam, sometimes pushing right through the stitching.
The reverse case exists as well. A strip that has taken a set from heat is effectively longer along its curve than a straight channel can accommodate, so it bows outward and lifts the seam away from the rest of the garment in a visible arc. Either way the cause is two materials that no longer match each other.
Water and a hot dryer together
Taken separately, each stage is survivable. A cool wash wets the channel and the face fabric, both shrink a little, and a garment dried flat in open air will usually settle back into something close to its original line. Heat on its own, with no water involved, mostly affects the strip and leaves the channel where it was.
Together they do the real damage, and in a specific order. Water shrinks the channel and softens the stitching. The garment then goes into a dryer, where the strip is heated into the rubbery range while the shrunken channel is holding it in a tighter curve than it was ever built for. It cools in that curve and sets there.
Nothing after that reverses it. A strip of plastic boning cannot be unset by washing, by hanging, by weight or by patience. Replacing it means opening the channel, pulling the old strip out and fitting a new one, which is straightforward for somebody who sews and impossible from outside the garment.
So the sequence worth breaking is heat after water. Washing a structured garment in cool water, laying it flat or hanging it with its weight supported, and letting it dry in air keeps the strip well out of the range where it changes. It may need pressing afterward, but press the cloth and work around the channels rather than over them.
Structured garments in Denver closets
Denver air is dry, and dry air is kinder to a structured garment than damp air is, because a garment that dries all the way through is less likely to go back into a closet with moisture still sitting in a channel. The dryness does nothing at all, though, about what a hot cycle does to a strip of plastic in a seam.
These garments come out for the gatherings and the evenings out that this season brings, then go away again for a long stretch. A garment stored hanging keeps its line. One folded into a box has its strips bent for the entire time it is in there, and a strip held in a bend in a warm room will slowly take some of that bend for good.
WaveMAX Denver is on East Hampden Avenue, and the useful thing here is being able to keep one structured piece out of a hot cycle while everything else goes through normally. The rest of what you wore, the shirts, the knitwear and the washable layers, is ordinary laundry. The garment with strips in its seams is not.
Everything except the structured piece
Most of what gathers in a basket after a season of evenings out is straightforward: shirts, knitwear, trousers and all the washable layers that went underneath. Those go through on a sensible cycle in a drum with room to spare. The structured garment comes out of that pile first and gets handled on its own terms.
The machines at our self-service laundry on East Hampden Avenue cover everything in the pile except the structured piece, which is the whole reason for sorting it out first, and the range of drum sizes means a heavy coat or a stack of knitwear never has to share a cycle with something that needs a cool one.
Our machines and the store are cleaned daily.
Nou wash-dry-fold service covers the everyday laundry.
For general guidance, The American Cleaning Institute publishes a fabric care guide that is a useful cross-check.
The short version
Boning is a stiff strip in a channel, put there to stop a seam collapsing under the pull of the cloth. The plastic kind is thermoplastic, so heat softens it and it hardens again in whatever shape it was bent into. The cotton channel around it shrinks in water while the strip does not, so the strip ends up standing proud of the seam. Wash cool, dry in air, and keep an iron off the channels.
WaveMAX Denver is at 10005-A E Hampden Ave, easy to reach from Denver and the surrounding area. If you have a load that will not fit at home, we have the machines for it.