In Old English, cob was a root word which meant lump or rounded mass. Cob houses are made of clay-like lumps of soil, sand and straw. Unlike adobe and straw bale construction, cob does not use bricks or blocks. Instead, wall surfaces can be sculpted into smooth, sinuous forms. A cob home may have sloping walls, arches and lots of wall niches.

Cob homes are possibly the most practical form of earth architecture. Because the mud mixture is porous, it withstands long periods of rain without weakening. A plaster made of lime and sand may be used to windproof the exterior walls from wind damage. Cob houses are suitable for the desert or for very cold climates.

What is Cob?
The Down To Earth Building Bee offers photos and definitions.

Cob Homes: Groundworks
How to build your own cob home. Workshops, handbooks, and more.

Building With Cob
Detailed chronicle of the construction of a Cob Home, from Mother Earth News.