A straw bale is a large bundle of straw tightly bound with twine or wire. Bales may be square, rectangular, or round, depending on the type of baler used.

Small square bales are sometimes used to build or insulate houses. Because bales are tightly compressed, the final plastered walls offer excellent thermal mass, good structural strength, and low flammability. They also make extremely efficient insulation, far in excess of North American building codes, and are therefore gaining popularity as part of passive solar and other renewable energy projects.

See straw-bale construction.