Why Do Clothes Get Wrinkled, and How Does Ironing Get the Wrinkles Out?

Your clothes get wrinkled because you insist on putting them on a warm, moist, moving body. If you were cold, dry and motionless, you’d have no problem. No clothing problems, anyway.

It’s heat and moisture that put the wrinkles in, and it’s heat and moisture that are going to get them out. Dry, cold pressing, even with tons of pressure, will accomplish little; you need both the heat and the moisture that did the original damage.

It’s hard to make generalizations about wrinkling and ironing, because there are so many different kinds of fibers that our clothes are made of these days. There are the synthetic (man-made) fibers, including nylon and a variety of polyesters and acrylics with various trade names.

The synthetics are all chemicals known as polymers: materials that are made up of huge molecules, each of which consists of thousands of identical, smaller molecules, all strung together into enormously long (for a molecule) chains. Many of these synthetic fibers are sensitive to heat. That is, when heated they bend and when they cool they retain the bend. If that is done to a garment at the factory, it will keep its shape.

On the other hand, there are the natural fibers taken from plants, animals and insects, including cotton from the cotton plant, linen from flax, wool from various animals and silk from worms. I’ll concentrate on one of the oldest and most wrinkle-prone of all the fibers: cotton. As far as wrinkling is concerned, it’s one bad actor.

Cotton fibers are filaments of cellulose, a natural polymer that occurs in plant cells. (To split hairs, so to speak, a fiber is a single unit of cotton that is at least a hundred times as long as it is wide, while a filament is an extra-long fiber, a strand is made up of many filaments and a thread is made of many twisted-together filaments. I knew you’d want to know.)

A cotton fiber acts somewhat like a long, thin bar of metal, in that when bent slightly it will spring back to its original shape, but it can be bent only so far before it will stay bent. The amount of bending it can stand before retaining the crimp depends on the temperature. There is a certain temperature below which it will spring back and above which it will stay bent. For dry cotton, this so-called transition temperature is about 120 degrees Fahrenheit (49 degrees Celsius).

So far, you’re lucky, because your body temperature is only around 99 degrees Fahrenheit (37 degrees Celsius), well below the crimping temperature.

But then there’s the effect of moisture. Water, in the form of perspiration, for example, can lower the transition temperature of cotton down to around 70 degrees Fahrenheit (21 degrees Celsius). And whether you know it or not, you are always perspiring. You don’t usually notice it because the perspiration evaporates from your skin as fast as it is produced, unless, of course, the air is very humid, in which case it doesn’t evaporate and you say that you are “sweating.”

So now if you actually have the audacity to sit on your pants or skirt, or to stress your other apparel by sharply bending your warm, moist limbs, the fibers can be bent into new, crooked shapes. Then when you stand up, your perspiration evaporates and the fibers cool down below their transition temperature and stay in those new shapes. Your clothes are wrinkled and you are rumpled.

How do you get the fibers back to their original, straight shapes? Just give them heat and moisture again, to get them above the transition temperature while you hold the fabric in its original flat shape with the sole plate of a steam iron. The steam lowers the transition temperature way below the temperature of the iron, so the original, straight shapes can reform.

An easy way to think of all this is that heat and moisture “melt” the structure of the fibers, and when they cool their shapes “freeze,” whether those shapes happen to be straight or crooked.

In the laundry, always try to remove your clothes from the dryer while they are still warm and slightly damp. In that condition you can lay them out flat and they’ll cool into that flat shape. Or you can hang them up and let gravity pull them flat. But if you leave them in the dryer too long after it stops, the clothes will cool down in their jumbled positions and the wrinkles will be set.

Why is there a certain temperature above which cotton begins to wrinkle?

Cotton is made of cellulose, a natural polymer whose molecules consist of thousands of sugar (glucose) molecules, joined together into long chains. Cotton fibers are bundles of these cellulose molecules, all lying alongside one another in the direction of the fiber.

Here and there, the cellulose molecules are weakly bonded to one another sideways by so-called hydrogen bonds, which tie them together like a loose bundle of sticks. The trick is to keep them that way, because if those weak bonds are broken and reformed while the fibers are bent, they will stay bent.

Hydrogen bonds can be broken by a combination of heat, which makes the molecules jiggle, and water, which swells the fibers by getting between the molecules. Water lowers the transition temperature because when the fibers are swollen the molecules are farther apart and easier to separate.

That’s why a steam iron works so much better than a dry one.