• Divides air space to reduce heat transfer by convection
• Reduces heat transfer by radiation

Heat always moves from warm to cool by conduction, convection and radiation. Still air does not conduct heat well but, in a large space, such as a wall cavity, heat is lost by convection and radiation. Insulation forms the most significant piece of the Thermal Control Layer by dividing the air space into many small pockets of still air; this inhibits heat transfer by convection. At the same time, radiation across the space is reduced. This Thermal Control Layer is often referred to as the Thermal Barrier.