How Dry Cleaning Works

How Clothes Get Clean Without Water

Dry cleaning isn't actually a dry process. It just doesn't involve water.
Dry cleaning isn't actually a dry process. It just doesn't involve water. Graeme Nicholson / Getty Images

Dry cleaning is a process used to clean clothing and other textiles using a solvent other than water. Contrary to what the name suggests, dry cleaning isn't actually dry. Clothes are soaked in a liquid solvent, agitated, and spun to remove the solvent. The process is much like what occurs using a regular commercial washing machine, with a few differences that mainly have to do with recycling the solvent so it can be reused rather than released into the environment.

Dry cleaning is a somewhat controversial process because the chlorocarbons used as modern solvents can affect the environment if they are released. Some solvents are toxic and/or flammable.

Dry Cleaning Solvents

Water is often called the universal solvent, but it doesn't really dissolve everything. Detergents and enzymes are used to lift greasy and protein-based stains. Yet, even though water can be the basis for a good all-purpose cleaner, it has one property that makes it undesirable for use on delicate fabrics and natural fibers. Water is a polar molecule, so it interacts with polar groups in fabrics, causing the fibers to swell and stretch during laundering. While drying the fabric removes the water, the fiber may be unable to return to its original shape. Another problem with water is that high temperatures (hot water) may be needed to extract some stains, potentially damaging the fabric.

Dry cleaning solvents, on the other hand, are nonpolar molecules. These molecules interact with stains without affecting the fibers. As with washing in water, mechanical agitation and friction lift the stains away from the fabric, so they are removed with the solvent.

In the 19th century, petroleum-based solvents were used for commercial dry cleaning, including gasoline, turpentine, and mineral spirits.

While these chemicals were effective, they were also flammable. Although it wasn't known at the time, the petroleum-based chemicals also presented a health risk.

In the mid-1930s, chlorinated solvents began to replace petroleum solvents. Perchloroethylene (PCE, "perc", or tetrachloroethylene) came into use. PCE is a stable, nonflammable, cost-effective chemical, compatible with most fibers and easy to recycle. PCE is superior to water for oily stains, but it can cause color bleeding and loss. The toxicity of PCE is relatively low, but it is classified as a toxic chemical by the state of California and is being phased out of use. PCE remains in use by much of the industry today.

Other solvents are also in use. About 10% of the market uses hydrocarbons (e.g., DF-2000, EcoSolv, Pure Dry), which are flammable and less effective than PCE, but less likely to damage textiles. Approximately 10-15% of the market uses trichloroethane, which is carcinogenic and also more aggressive than PCE.

Supercritical carbon dioxide is nontoxic and less active as a greenhouse gas, but not as effective at removing stains as PCE. Freon-113, brominated solvents, (DrySolv, Fabrisolv), liquid silicone, and dibutoxymethane (SolvonK4) are other solvents that may be used for dry cleaning.

The Dry Cleaning Process

When you drop off clothes at the dry cleaner, a lot happens before you pick them up all fresh and clean in their individual plastic bags.

  1. First, garments are examined. Some stains may require pre-treatment. Pockets are checked for loose items. Sometimes buttons and trim need to be removed before washing because they are too delicate for the process or would be damaged by the solvent. Coatings on sequins, for example, may be removed by organic solvents.
  2. Perchloroethylene is about 70% heavier than water (density of 1.7 g/cm3), so dry cleaning clothes isn't gentle. Textiles that are very delicate, loose, or liable to shed fibers or dye are placed into mesh bags to support and protect them.
  3. A modern dry cleaning machine looks a lot like a normal washing machine. Clothes are loaded into the machine. The solvent is added to the machine, sometimes containing an additional surfactant "soap" to aid stain removal. The length of the wash cycle depends on the solvent and soiling, typically ranging from 8-15 minutes for PCE and at least 25 minutes for a hydrocarbon solvent.
  1. When the wash cycle is completed, the washing solvent is removed and a rinse cycle starts with fresh solvent. The rinse helps prevent dye and soil particles from depositing back onto the garments.
  2. The extraction process follows the rinse cycle. Most of the solvent drains from the washing chamber. The basket is spun at about 350-450 rpm to spin out most of the remaining liquid.
  3. Up to this point, dry cleaning occurs at room temperature. However, the drying cycle introduces heat. Garments are tumble dried in warm air (60–63 °C/140–145 °F). The exhaust air is passed through a chiller to condense out residual solvent vapor. In this way, about 99.99% of solvent is recovered and recycled to be used again. Before closed air systems came into use, the solvent was vented to the environment.
  4. After drying there is an aeration cycle using cool outside air. This air passes through an activated carbon and resin filter to capture any leftover solvent.
  5. Finally, trim is reattached, as needed, and clothes are pressed and placed in thin plastic garment bags.