Expanded clay pebbles known by many as LECA (Light Weight Clay Aggragate) are much more well known in Europe than in the U.S. Europeans use them in a very popular form of hydroponics known as hydroculture.
The leca (generic use of the word) on the left is Hydroton and dominates the U.S. market in the world of hydroponics (mostly pot and orchid growers currently).
The leca on the right is what I much prefer but can no longer find online in the U.S. market. They are B'Cuzz Grow Rokz by Atami. I think of them as "organic" expanded clay pebbles because they do not look manufactured like the smooth and uniformly rounded Hydroton. They look more natural in clear containers. They also do not roll around all over the floor when you spill them, and you will. Other than that there is probably no functional difference between the two regarding air and water exchange.
I would probably not use artificial soil mix for indoor plants except for the fact that CuGreen does applied research on plants in soil mix for the U.S. market. In my view (and that of must Europeans) hydroculture is a far superior method for growing plants indoors. It is a better way to supply oxygen to the plants, it is hygienic and much more user friendly regarding plant care.
The two inhibitions to the use of clay pebbles in the U.S. market are lack of education and shipping cost. Shipping can cost more then the pebbles so it is best to find a brick and mortar retailer rather than online. Over and above the domestic shipping cost, the pebbles are all imported from Europe. To the best of my knowledge, there are no clay pebble kilns in North America.
There is a higher intial cost compared to artificial soil mix, but expanded clay pebbles are a sustainable product. You can wash them in a diluted bleach solution and use them over and over again.
I would highly recommend them instead of soil based plants in perhaps pretty but rather dumb, drain hole clay pots. Once you get the hang of it, you will kill far fewer houseplants and those you grow will be much more healthy.
ScienceDaily (Mar. 16, 2011) — In the business of concrete making, what's old -- even ancient -- is new again.
Almost 1,900 years ago, the Romans built what continues to be the world's largest unreinforced solid concrete dome in the world -- the Pantheon. The secret, probably unknown to the Emperor Hadrian's engineers at the time, was that the lightweight concrete used to build the dome had set and hardened from the inside out. This internal curing process enhanced the material's strength, durability, resistance to cracking, and other properties so that the Pantheon continues to be used for special events to this day.
But it is only within the last decade or so that internally cured concrete has begun to have an impact on modern world infrastructure. Increasingly, internally cured concrete is being used in the construction of bridge decks, pavements, parking structures, water tanks, and railway yards, according to a review of the current status of the new (or old) concrete technology just published by the National Institute of Standards and Technology (NIST).