Dry cleaning involves liquid, agitation and a spin cycle much like laundry. What makes it dry is the absence of water, and that single substitution explains most of what the process can and cannot do.
A solvent replaces water
Garments go into a machine resembling a large front-loading washer, which fills with a chemical solvent instead of water and tumbles the load.
The solvent dissolves oils, greases and body soils. It then drains, is filtered and distilled, and is reused rather than discarded after each load.
That recovery loop is central to the economics of the business and is also why solvent handling is a regulated part of the operation.
Water is what damages certain fabrics
Natural fibers such as wool absorb water and swell, and the mechanical action of a conventional wash then causes the fibers to lock together and shrink.
Structured garments have interfacing, padding and linings made of different materials that shrink at different rates, which is what warps a jacket in a home machine.
A solvent does not swell fibers the same way, so shape and drape survive a process that water would ruin.
The tradeoff shows up in stains
Because the solvent targets oils, it handles grease well. Water-based stains such as coffee, wine or perspiration are the ones it addresses least effectively on its own.
Cleaners therefore pretreat by hand at a spotting board, applying specific agents to specific stains before the garment enters the machine.
This is why telling the counter staff what a stain is matters. An untreated water-based stain can pass through the cycle essentially unchanged and then be set by heat.
Finishing is a separate craft
After cleaning, garments are pressed on forms and specialized presses shaped for shoulders, sleeves and trousers, using steam and controlled pressure.
Much of what customers perceive as cleaning quality is actually finishing quality. The crispness of a returned shirt comes from this stage.
Many cleaners also launder shirts conventionally in water and then press them, so a single ticket can include both processes.
Care labels encode the manufacturer's test
A garment's care label reflects what the manufacturer validated, not the only method that could possibly work. Labels are conservative by design.
Cleaners generally follow the label because deviating shifts liability onto them if a garment is damaged.
Where a garment combines materials with conflicting requirements, such as a leather trim on a wool coat, the cleaner is making a judgment call, and asking about it beforehand is reasonable.