Air drying clay and air clay are the same material sold under whichever name the packaging chose, and the variation in spelling is not a variation in product. It is a clay body with a binder that stiffens as water leaves it, so it hardens at room temperature and never becomes ceramic. Knowing that one fact settles almost every question people ask about it.
Why the same product has three names
Manufacturers and retailers label this material as air dry clay, air drying clay and air clay more or less interchangeably, and the search volume splits across all three because buyers copy whichever phrase they saw first. There is no technical distinction hiding in the naming. What does vary between brands is the binder, the fineness of the clay and whether the body is bulked with fibre, and none of that is signalled by the name on the front of the packet. Read the description rather than the noun.
What the binder does, and what it cannot do
In a fired body the strength comes from the kiln: particles fuse at temperature and the object becomes a new material. In an air drying body the strength comes from the binder holding clay particles together as the water evaporates. That makes it strong enough to handle, paint and display, and it leaves the object soluble in the way a fired pot never is. Soak a dried air-clay piece and it will soften. That is the specification rather than a defect, and it decides every use.
Buying it by the packet or by the bag
Air drying clay is sold two ways and the price difference is large. Craft shops sell small packets at craft prices, which is the right purchase for one project. The pottery suppliers priced on this site sell it by the bag alongside their fired bodies, which is what a school, a class or anyone making repeatedly should buy. The per-kilogram difference between the two routes is bigger than the difference between any two brands.
The dust rule applies here too
Wet clay in a bag is harmless to handle. Dried air clay sanded, filed or swept releases the same respirable crystalline silica that the fired side of this hobby manages carefully, and this material is sold heavily into schools where nobody expects a hazard. Sand wet rather than dry, wipe surfaces instead of brushing them, and the risk goes away for the price of a sponge.
Questions people ask about air drying clay
Is air clay different from air dry clay?
No. They are the same category of product and the names are used interchangeably by manufacturers. Differences between brands are in the binder and the fineness of the clay, not in the name.
Can air drying clay be fired?
Some bodies sold as air drying are genuine clay with a binder and can be fired, and some are not clay at all. Only the manufacturer's own description settles it, and if it does not say, assume not.
How strong is it once dry?
Strong enough to handle and display, and weaker than fired ceramic in every direction. It will chip on a hard floor and it will soften if it gets soaked.