You may find that vapour barriers are often not required in warmer climates. And, if installed in the wrong climate or on the wrong side of building materials, a vapour barrier can cause more harm than good. This circumstance may prevent water vapour from drying, which in turn can cause rot and mold. (Source: Dupont.)

Radiant Barrier Moisture Problems The other main issue that can impact the performance of any radiant barrier is moisture. In colder weather, radiant barriers can sometimes develop condensation. This issue is most prevalent in climates where the temperature regularly falls below zero degrees Fahrenheit.

The R-value per unit of a barrier's exposed surface area measures the absolute thermal resistance of the barrier. , quantifies the temperature difference per unit of heat flow rate needed to sustain one unit of heat flow rate.

Some studies show that radiant barriers can reduce cooling costs 5% to 10% when used in a warm, sunny climate. The reduced heat gain may even allow for a smaller air conditioning system. In cool climates, however, it's usually more cost-effective to install more thermal insulation than to add a radiant barrier.