1. The problem statement, all variables and given/known data The textbook claims 'An air caivty between a brick outer wall and the inside wall helps to insulate from heat and cold.' It asks to explain in terms of heat conduction. 2. Relevant equations none 3. The attempt at a solution Is it because it takes a certain amount of energy to get the conduction in the brick going as a brick is a poor conductor. Once it starts rolling or conducting than it becomes hard to stop it. So by installing a cavity, this momentum of conduction in the brick is stopped and for conduction to occur again, the air molecules must break a certain energy level which is hard to attain in this small cavity.