Dry cleaning involves immersing garments in liquid, agitating them and spinning them, much like laundering. The difference is that the liquid is a solvent rather than water, and that single substitution explains why certain fabrics require it.
Water is the problem, not the dirt
Natural fibers such as wool absorb water and swell, and agitation while swollen causes the scales on wool fibers to interlock permanently.
That interlocking is felting, and it is why a wool sweater emerges from a washing machine smaller and denser than it went in.
Water also relaxes the structure that tailoring builds into a garment, which is why linings, interfacings and pleats lose their shape after machine washing.
Solvent removes what water cannot
Body oils, grease and many cosmetic stains are not water soluble, which is why they persist through ordinary washing without detergent action.
A nonpolar solvent dissolves those oils directly, lifting them from the fiber without the mechanical scrubbing that water-based washing requires.
Water-soluble stains are the reverse case. Sugar, coffee and perspiration respond poorly to solvent and are treated by hand before the garment enters the machine.
The machine recycles its solvent
A dry cleaning machine washes, extracts and dries within a single sealed drum rather than moving garments between appliances.
Solvent is continuously filtered and distilled during the cycle, so the same liquid is reused across many loads rather than discharged.
This closed loop exists for cost and environmental reasons together, since solvent is expensive and its release is regulated.
Pretreatment does most of the visible work
Before a garment enters the machine it is inspected, and identified stains are treated individually with agents chosen for the stain type and fabric.
This is where a customer's description matters, since an unidentified stain may be treated with the wrong agent or set permanently by the drying cycle.
Heat sets protein and sugar stains, so an untreated spot that survives the cycle is considerably harder to remove afterward.
Finishing is a separate craft
After cleaning, garments are pressed on shaped forms that restore structure rather than simply flattening fabric.
Steam relaxes fibers, the form imposes the intended shape and cooling sets it, which is why professionally finished garments hang differently from home-ironed ones.
Much of what customers perceive as cleanliness is actually this finishing, and it is the part that is hardest to reproduce at home regardless of what solvent or detergent is used.