You may have heard that insulation works by trapping air. “Dead air pockets” is the term often used. So, the next question is: Why doesn't the large dead air pocket in an uninsulated wall cavity reduce heat flow as well? It’s true that uninsulated walls really do transfer more heat, not less.

The answer lies in the size of the dead air pocket because of convective loops. In an uninsulated wall cavity, the air moves in a cycle around the cavity ... (Energy Vanguard)

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