What does it mean that straw bale walls “breathe”?

Bale walls do not breathe in the sense of allowing air to move through the walls. In fact, it is a good idea to limit air infiltration into the walls as air carries moisture. When we say they breathe, we are referring to the movement of moisture through, and out of, the walls. It is critical that moisture moves out of the walls. Permeable plasters such as Lime or Earth should be used in wet or humid climates and Cement based plasters should only be used in dry climate climates, if at all. This transfer of moisture improves indoor air quality without sacrificing energy efficiency and keeps the bales dry. Straw is a natural material, and as such it does not off gas the way conventional insulations do, adding to the health of the home and its occupants.  more