How do cavity walls use an air space between layers of brick?

A cavity wall is a construction technique consisting of two vertical layers of masonry, known as wythes, separated by an air space and connected by metal ties. This design serves two primary functions:1

• Thermal Insulation: The air space significantly improves energy efficiency by reducing the heat-flow rate to approximately 50 percent that of a solid wall, making it highly effective for buildings in colder climates.12
• Moisture Management: The cavity acts as a drainage system, allowing any moisture that penetrates the exterior layer of brick to drain away safely, which helps protect the building's structural integrity.1

This method is utilized both for bearing-wall construction and as non-load-bearing infill for framed structures.1