|Style over substance|
A laundry ball is a ball-shaped object said to clean clothes by mechanical action when used in a washing machine, obviating the need for detergent. Tests have shown they don't work any better than plain water. They are often sold by multilevel marketing operations.
There are two motives for this over conventional and orthodox cleaning methods; 1) you protect the environment from all those nasty surfactant chemicals and 2) you save money by not having to buy all those nasty surfactant chemicals. These are indeed real benefits of laundry balls - well, barring any nasty chemicals used in their manufacture, marketing, packaging and transportation - but as they most certainly don't work. So it's up to the individual whether they want to use them instead of actual cleaning products.
All it really does is make you smell like sweaty mildew since your clothes never really get clean, which becomes progressively worse.
While sticking a ball into a washing machine to "agitate" the clothing may work - indeed, increased agitation is the reason that the (now mostly defunct) Dyson washing machine had better performance - "Laundry Balls" have far more woo centered explanations for how they work. Some washing ball products contain "washing pearls". These are small ceramic balls which supposedly "interact" with the washing water or release substances into the water - possibly this is an example of a homeopathic detergent. Actual details of the science behind these laundry balls are few and far between, and as with most woo, when methods are kept secret, alarm bells usually start sounding in skeptical heads. Usually both types of balls are marketed as "environmentally friendly" alternatives to ordinary washing powders or liquids. They are claimed to be able to wash several hundred, up to 1000-1500 loads of wash until they should be discarded.
 Infrared and alkalization
“”...The powerful far-infrared rays... break water molecule's hydrogen-combinations into small clusters and force the small water cluster being activated to increase it's molecular motions, penetration force, and washing power.
|—One of among many bullshit claims.|
One of the claims that is commonly made by makers of laundry balls is that they emit infrared waves which supposedly effect the washing by cutting off the hydrogen and binding factors of water molecules. The claim of emitting infrared is not false, as such, as all materials emit "far infrared waves" - in other words, blackbody radiation. It is also true that heating reduces the surface tension of water. Importantly, however, the effect of the radiation emitted by the pearls is negligible compared to the radiation emitted by the water which is being heated. There are no independent tests showing that the pearls could generate stronger infrared waves by interacting with water than what they otherwise should. This is basically a case of taking very "scientific" sounding words that confuse the audience - the same trick is done with foot pads that contain "hydrolyzed cellulose" as an ingredient, rather than "sugar".
The claim of alkalization is dubious. While it is true that the alkaline agents in normal washing powders catalyze the tensides, there are no studies suggesting that the washing pearls would affect the pH of the water, especially for a duration of several thousand washes. The pH of water is not just some magical property, it is caused by ions dissolving in water; to affect the pH significantly, these "pearls" would have to dissolve quite a proportion of their material into the water, and if they could dissolve to that degree, you'd be lucky to get one wash, never mind a thousand.
 Anti-chlorine and antibacterial properties
Many products also claim that the pearls contain "anti-chlorine" agents which are supposed to neutralize chlorine which has been added to the tap water - again, what these "agents" are is never really revealed, and you can't just magically remove chlorine from water, the ions would have to react and go somewhere. Chloride and bleach related substances are actually common in washing powders and chlorine is used in the disinfection of tap water. The claims state that by removing chlorine from the washing water the surface tension is (again) reduced and harmful chlorine can't interact with the clothes, even though the amounts in tap water are very small both in Europe (0.3-1.0 ml/l) and North-America (4 ml/l).
Chlorine is a strong antibacterial agent, so neutralizing it from the washing water is, in fact, illogical if you want to maintain antibacterial properties. There are no clear explanations of how the antibacterial substitute in the pearls work - apart from bullshit. A viable option would be silver pearls, as silver has documented antibacterial properties, but that would be highly unlikely to make an appearance in these products.
 Magnetic properties
Some products claim to have magnetic elements which "minimizes the size of the water molecule which helps with scale and rust removal of the washing machine and pipes". The amount of bullshit in that phrase cannot be emphasised enough, making water molecules smaller would make any chemist laugh, or possibly start thinking about complex and ingenious ways to really achieve such a feat. Both claims are false from a proven scientific viewpoint; while magnets do interact with rust (the iron still has magnetic properties even when oxidised), magnets will not keep rust out of your laundry, and molecules can't be "scaled" freely.
This claim is basically another instance of structure-altered water.
 Negative ions
Some laundry balls claim to release negative ions, which cause the dirt to weaken in its adherence to the fabric. It is possible that OH- (hydroxide ions) could be created, but not in a large quantity. Again, like with many of the above examples, such ions (which would affect pH as described above) need to come from somewhere as if these balls really do last for hundreds of washes, they won't be leaking out many of these ions. It would be possible if the balls were solid supported base catalysts that produced OH- by abstracting H+ from water molecules, but this would require the balls to be "recharged" after every use by flushing them with a base like potassium hydroxide, and this isn't the case. Besides, this method would mean you'd be washing your clothes in a base-bath, and you want clean clothes, not rags when you're finished, right?
Laundry balls were once sold by a Scientologist-owned company called Trade-Net. However, due to fraudulent advertising the company was forced to pay large fines to various US states, and it promptly collapsed.
- Skeptic.com - Laundy balls and discs, too good to be true?
- The Straight Dope - Do laundry balls really work?