Hypertufa is a mixture of Portland cement, peat moss, and then a combination of other things, including sand, perlite and vermiculite. Water is added to the mixture until it is a consistency that can be "packed" like a snow ball. Then it can be molded or shaped into a variety of items, usually garden planters and garden ornaments.
The hypertufa items must be cured in a moist environment (plastic bag and water) for several weeks and then they need to be neutralized with vinegar or at least multiple rinsings with water. Then they can be used in the garden.
Here are the items I completed in class.
Hypertufa is meant to be rather rustic and resembles stone. It is somewhat lighter than stone, especially if it contains a fair amount of peat moss and vermiculite/perlite... but remember, once it is filled with soil and plants, it will be pretty darn heavy! It is supposed to be able to withstand a wide temperature range without cracking, so can be kept outdoors year round. 
