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I got the idea to do a science of laundry series on the blog when I was at the RDIA (Real Diaper Industry Association) meeting. We had a Laundry Science presentation which I thought was very interesting; and judging by all the non-laundry normal people that also thought it was interesting, I decided I’d do a very in-depth look at what goes on when you do the laundry. There’s quite a lot going on, actually!

Let’s start with the basics.

Both front loading and top loading machines work on the same principles of cleaning. Proper washing depends on the following factors:

Mechanical Action – Mechanical action is the machine moving your clothes around. As the clothes rub up against each other. Agitation dislodges stains. If you over-load your machine your clothes won’t get the agitation needed to take stains out, and if you under-load there may not be enough to rub up against.

Chemical action – This is the reactions between the soap, soil, and water to remove stains from clothing. For washing purposes, a chemical is the cleaning agent that is added to the water. Saponin, the cleaning agent in soap nuts and our liquid detergent is a chemical – it’s just made by a plant instead of by people. Either way, a washing chemical is necessary to get stains out.

Heat/Temperature – heat will speed up the chemical reaction of the soap. For every 10 degree (F) drop in temperature below 115F there is a 15% reduction in the chemical reaction, which is why washing in warm or hot is preferable to getting things clean and why many washing machine and detergent companies suggest you launder in the hottest temperature the care label recommends.

Time – The length of the wash cycle in which the garments agitate in the conditions dictated by temperature and chemicals.

Simply put, the longer the laundry is exposed to heat, cleaning chemicals and mechanical action, the cleaner it will be.

For you cold water washers – if you want to wash in cold, your washing machine will require a longer wash cycle (more time = more agitation) to make up for the temperature loss as well as more chemicals to get the same result as warm water washing. If you want to wash in cold water with the same amount of chemicals, then you need to add even more time and agitation, etc. Also something to know for cold water washing is that certain fabrics (namely, cotton) will soak up more water when wet. Cold water weighs more, so it may require a longer dry cycle as well.

Wash Cycle Steps:

Pre-Rinse – This can be done with water alone but a little bit of detergent will start the initial soil release. Hot water on a pre-rinse can set stains, but warm is better than cold, especially when washing articles that have body fluids on them (sweat, urine, etc) as those are most soluble at body temperature. Most busy people will just add the detergent at the beginning of this phase for the entire wash. Not all washing machines will have this as a setting/phase. If your machine has a compartment for detergent, it will usually wait to add the detergent until the end of the pre-rinse cycle when the machine is full of water already.

Wash Cycle – The wash cycle is where the main mechanical action takes place. The wash cycle works best when there is a chemical added to release soil, as well. There are two main categories of chemicals for washing:

Surfactants change the surface tension of the water. What this means is that water can more easily penetrate the fabric fibers which loosens the dirt and then holds it in suspension in the water. They are shaped like a tadpole with the head being water loving and the tail being water hating (and dirt attracted). The surfactant molecules will surround a dirt particle, break it up, and force it away from the fabric surface, holding it in suspension in the water until it’s rinsed away. I have a whole post on surfactants coming up which will explain everything. There are naturally occurring surfactants (like those in soap nuts) and surfactants derived from petrochemicals as well.


Some detergents also contain enzymes. These are specialized to “eat away” at specific soils like proteins, fats/oils and starches. Some enzymes can irritate sensitive skin. Laundry detergents with a high amount of enzymes (often labeled “carezymes” to help keep pilling to a minimum or prevent it) can contribute to holes wearing in cotton fabrics (like the holes in your denim jeans that appear out of nowhere). Enzymes are great for difficult stains and are what’s in many stain sticks and stain removers. Personally, I advocate only using them directly on stains as needed to extend the life and wearability of your clothes as opposed to using them in every wash.

Bleaching is the next step if it’s something you’re going to add. (Oxygen bleach is color safe and better for the environment and much easier on your clothes). If your machine is a top loader and full of water, you can dump in some oxygen bleach, lift up the washing machine lid which will stop the washing and let it soak for a few hours before closing the lid and resuming the wash. Hot water is best for oxygen bleach because it speeds up the chemical reaction which can take longer with oxygen bleach.

Rinse Cycle – Rinsing removes all residual soil and washing agents/chemicals. A Warm rinse is better because it releases more residues. Also, clothes (especially cotton) can hold onto more cold water (which weighs more!) so your spin cycle is more effective in getting more water out if it’s warm. Sometimes an extra rinse cycle is necessary if the items were particularly soiled or if too much soap was used.

If you’re washing something more complicated like diapers, there can be extra steps (more rinses, etc) but this is a general for all laundry in a home washing setting.


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