Dry Cleaning

Kevin Bralten
Feb 6, 2018 · 5 min read

Dry Cleaning is a seemingly mysterious topic — there’s a place and you take clothes there and then you pick up clean clothes. But what is it, how does it work, and why do some clothes require it?

Let’s start with the easiest to unpack, what is dry cleaning? It is cleaning, but it’s not “dry”, although it doesn’t traditionally use water. Broadly speaking, dry cleaning would be better described as “not hot cleaning”, it encompasses a number of cleaning methods which don’t involve either hot cleaning liquids or heating the clothes to dry them after washing.

Dry cleaners as a business are a combination of several related garment cleaning services — garment cleaning itself, alterations and repair, customer-service, and often footwear cleaning. Although the trend is changing, most dry cleaning “locations” don’t actually do the cleaning on-site, instead the garments are ingested and sent for cleaning, then held for pickup. In addition to removing the need to manage machines on-site, the plant-based process means there’s always a steady flow of garments for cleaning and with a larger pool of garments, more specialized equipment can be used instead of generalist machines.

The dry stores were pick up and drop off locations. Garments from these locations were picked up three times a day and taken back to the plant for processing.

The iconic hanger serpent dominating the retail presence isn’t anything magical, it’s just an efficient way to store and retrieve a large number of garments, it excels over rolling garment racks when you consider the variability in drop-off time and pickup-time which would either leave half-empty racks or require continuous rearranging.

A commercial dry cleaning machine

The dry cleaning cycle shares most of the process with the common washer-dryer:

There are two enormous differences between this process and traditional laundry though: the cleaning solution doesn’t use water and the washing and drying temperature is close to room temperature.

Tetrachloroethylene aka PERC

Unlike traditional laundry, which generally uses detergent dissolved in water, dry cleaning uses an undissolved solvent: typically chlorine based like PERC, petroleum based such as Stoddart Solvent, or even super critical Carbon Dioxide. All of these are better at dissolving grease, oil marks, and other organic deposits which makes them more effective cleaners for some stains, but the real reason they’re used is they all have significantly faster evaporation rates (higher vapor pressure) near room temperature, it’s this property which makes dry cleaning “work”.

The dry cleaning “wash” cycle occurs with room temperature solvents and, after a spin cycle, the air used for drying is only around 60℃ (which is cooler than home dryers) and more importantly only lasts a few minutes, which keeps the garments from becoming warm.

Keeping garments from getting warm while cleaning is, primarily, the reason for dry cleanings existence. The majority of dry clean only garments need special care because the fabric shrinks when heated, or worse, the garment is made of multiple fabrics which shrink differently when heated. A smaller subset is garments which would dissolve (like glued on sequins) or discolour when heated.

Not as common, but the solvents used in dry cleaning can prevent colour bleed — the colour either doesn’t dissolve as easily in the non-polar solvent or the dissolved colour doesn’t transfer back from the solvent to other parts of the garment.

For some types of stains, the solvent cleaners are more effective at removing the stain, but for other types (like the salts deposited from perspiration or deicing salt), hot water is a more effective cleaner.

Separated from the mechanics of the cleaning process, the dry cleaners staff are professional garment cleaners and they tend to actually go through all the cleaning options — spot treating, steaming, vacuuming, etc before declaring a stain untreatable. Depending on the garment, they’re also better at preparing the garment for washing (removing buttons, basting trim to keep it in place, etc).

If the tag says DRY-CLEAN ONLY, obey it. If it says DRY-CLEAN, that means that is the recommended method, not the only method.

Do you need to actually go to the dry cleaners? It depends. If washing the garment in room temperature water and air drying gives you the desired result, it’s a perfectly valid method — for a very small number of fabrics which are irreparably changed by water absorption (like suede), solvent cleaning is the only option.

So if this all sounded simple, it’s because the hardest part was glossed over. Dry cleaning as a concept is fairly simple — and it was simple in implementation until the late 20th century — but the complexity comes from handling the cleaning solution. Unlike water and detergent, the fresh cleaning solution is expensive and in a limited supply, the used cleaning solution can’t just be poured in the sanitary sewer, and the evaporated rinse can’t be vented to the atmosphere.

Shipping and storing the solvent is complicated by hazardous chemical restrictions, the machine needs dispensing equipment to pump the solvent into the wash chamber, the used solvent is filtered and re-used instead of being disposed of, and the evaporated solvent is drawn over a complex cooling and filtering apparatus to condense the solvent before venting.

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Kevin Bralten

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A generalist who solves problems by similarity using experience in wilderness education, logistics, electronics, mortgages, software, and metal recycling.

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