G

Glossary

Diffusion

The movement of individual molecules through a material. The movement occurs because of concentration gradients and (to a much lesser degree) thermal gradients, independent of airflow. A mode of water vapor transport in building enclosures that is much slower than airflow.

Related terms: Permeance

Related resources: BSI 049: Confusion About Diffusion; RR-0104: Solar Driven Moisture in Brick Veneer