There is a particular smell to washing that has dried outdoors, and a particular feel to it as well. The sheets are crisp. The white shirts look whiter than they did. The towels, unfortunately, feel like they have been starched and left in the sun, which is roughly what happened. All three of those results come from the same two things: ultraviolet light doing chemistry on the fabric, and water leaving the fiber without anything moving it around. One of them is doing you a favor and one of them is not.
What sunlight does to dye
Color in fabric comes from molecules built with a particular kind of structure, a run of alternating bonds that absorbs some wavelengths of light and reflects the rest. What reaches your eye is whatever was not absorbed. Ultraviolet light carries more energy per photon than visible light, enough to break those bonds outright, and a broken structure no longer absorbs anything.
That is why fading is not the same thing as washing out. Nothing has left the fabric. The dye is still there, sitting in the fiber, chemically wrecked and reflecting everything that hits it, which reads as pale. It also explains why fading is uneven. The side of the garment that faced the sun loses color and the side facing away does not, so a shirt hung the same way every time develops a light front and a darker back.
Not all dyes go at the same rate. Reactive dyes, which form an actual chemical bond with the cotton, hold up well. Direct dyes, which only cling to the fiber, go much sooner. Certain colors are weaker than others by their chemistry, which is why a red shirt turns pink and a black one goes brown rather than simply lighter: the components of the mixed shade break down at different speeds and the survivors set the new color.
The same process works in your favor on white cotton. The yellowing on an old white shirt is oxidized body oil and residue, and those compounds are colored for the same reason dye is colored. Sunlight breaks them apart just as readily. A white sheet hung out genuinely does come back whiter, and the effect is chemical rather than a trick of the light.
What sunlight does to the fiber
The energy that breaks dye molecules does not stop there. Cotton is cellulose, long chains of linked sugar units, and ultraviolet light cuts those chains. A shorter chain makes a weaker fiber. Nothing is visible while it is happening, because the fabric looks and feels the same, but the strength is going out of it with every exposure and the loss does not come back.
The result shows up years later as a tear that seems to come from nowhere. An old sheet splits along a fold line, or a pillowcase gives way in the middle where nothing was pulling on it. That fabric had been quietly weakened by exposure and finally reached the point where ordinary handling was more than it could take. Damage that accumulates without warning is the hardest kind to act on.
Protein fibers take it worse than cotton. Wool and silk yellow under ultraviolet as well as weaken, and silk in particular can lose a serious amount of its strength from a single long exposure. Nylon and elastane suffer too, which matters for anything with stretch in it, since the elastic threads fail first and the garment goes baggy while the outer fabric still looks new. Turning things inside out and hanging in shade handles most of this.
Why line dried towels go stiff
A towel works because of its pile: thousands of loops of loosely twisted cotton standing up off a woven base. Softness comes from those loops being separate, able to move against each other and trap air. Absorbency comes from the same thing, since water travels up the spaces between fibers. Anything that sticks the loops together takes away both properties at once.
Evaporation is what sticks them together. As a wet towel dries, the last water in it retreats into the narrow gaps between neighboring fibers, and the surface tension in those tiny bridges pulls the fibers toward each other. When the final trace of water goes, the fibers are left touching, and cellulose surfaces in direct contact form hydrogen bonds with each other. They are genuinely stuck. This is the same mechanism that turns wet paper pulp into a sheet of stiff card as it dries.
A tumble dryer prevents it by never letting the fabric sit still. The load lifts and falls continuously, and every fall flexes the pile, which breaks the bonds as they form and pushes the loops apart again. The towel finishes with its fibers separated because they were never allowed to settle against each other. It is mechanical work, not heat, that does it. A towel left motionless in a warm room comes out just as hard as one dried outside.
Two other things make it worse. Hard water leaves calcium and magnesium deposits between the fibers as it evaporates, which act as a mineral cement holding the loops where they landed. Detergent residue does the same with a sticky film. Both are cured by using less detergent and running an extra rinse, and a cup of white vinegar in the rinse dissolves mineral deposits without leaving anything behind.
What dries well outdoors and what does not
Sheets, tablecloths, linen and heavy cotton are the things that come back better for a day outside. All of them are fabrics where crispness is desirable rather than a fault, and all of them are flat pieces that dry evenly without anything to distort. Denim and canvas work well for the same reason, and both benefit from the sun bleaching a little of the surface off over time.
Towels, bathrobes and anything with a pile belong indoors, or at least belong finished indoors. So does fleece, where the raised surface behaves like a short pile and mats down for exactly the same reason. If a fabric is soft because its surface fibers stand apart, drying it still will make it hard.
Dark and saturated colors should stay out of direct sun, and that includes navy, black, red and anything dyed a strong single shade. Inside out helps, since the fading then happens on a face nobody sees, and the outer surface is shielded by the fabric itself. A shaded line or a covered porch gives most of the airflow with a fraction of the ultraviolet.
Technical fabric is the one most people forget. Waterproof coatings, printed graphics, elastic waistbands and anything with a stretch content all degrade under prolonged ultraviolet, and they degrade before the fabric they are attached to. A jacket that has lost its water resistance and a t-shirt whose print has cracked have usually spent a lot of their life on a line in full sun.
Getting the best of both
The useful compromise is to do most of the drying outdoors and finish the load with a short tumble. By the time a towel comes off the line it is dry and the bonds have already formed, but a few turns in a warm drum flexes them apart again and the pile stands back up. The sun did the work of drying. The drum did the work of softening.
Shaking a towel out hard before it goes on the line helps more than it sounds like it should. The snap separates loops that are lying against each other and lets them dry apart rather than together, so fewer bonds form in the first place. Hanging in moving air rather than still air does the same thing, since a breeze flexes the fabric continuously while it dries.
As the season turns and the sun drops lower, line drying gets slower and the ultraviolet load gets lighter, which suits dark clothes better than midsummer ever does. It also means the heavier washing of the holidays, the bedding and the towels and the table linen, arrives at the point in the year when outdoor drying is least able to keep up. Planning for that in advance saves a pile of damp laundry later.
Hanging Washing Out in Phoenix
Phoenix has more sun than almost anywhere, and that changes the arithmetic. Fabric dries outdoors here in a fraction of the time it would take in a damp climate, which is an advantage, but the ultraviolet dose over that period is high and it is concentrated. Colors that would last years on a line elsewhere give up noticeably sooner.
Dry air makes the stiffness worse as well. The sooner the water leaves, the more of it retreats into the gaps between fibers all at once, and the more fibers end up locked together when it goes. A towel dried in low humidity comes out harder than the same towel dried in humid air, which is why households here notice the problem more than most.
Dust is the third factor. Fine airborne dust settles on anything hanging outdoors in Phoenix, and a garment that is still slightly damp holds onto it. On dark fabric that shows as a dull gray cast that no amount of rewashing quite removes, because the particles have worked down between the fibers. Bringing things in before they are bone dry makes it worse rather than better.
Softness the Line Cannot Give
Sun is good at removing water and bad at leaving fabric soft, because softness comes from movement rather than heat. A drum that turns a load steadily for the whole cycle keeps the pile open and the fibers separated, which is the one thing a still line can never do, whatever the weather.
The machines at our self-service laundry on West Thomas Road sit alongside dryers big enough to take a full set of bedding and towels together, so a load that came off the line hard can be tumbled back to something soft without being washed all over again.
Our machines and the store are cleaned daily.
Our wash-dry-fold service covers the everyday laundry.
For general guidance, The American Cleaning Institute publishes a laundry basics guide that is a useful cross-check.
The short version
Sunlight does two jobs at once. It breaks apart the molecules that carry color, which fades dye and also whitens yellowed cotton, and it cuts the cellulose chains that give the fabric its strength. Meanwhile the stiffness in line drying comes from evaporation pulling fibers together and locking them there. Sheets and linen gain from a day outside. Towels and anything with a pile need movement to stay soft.
WaveMAX Phoenix is at 6544 W. Thomas Rd., Suite 23, easy to reach from Phoenix and the surrounding area. If you have a load that will not fit at home, call us at 480-278-9685.