What are the differences between aluminum foil facing with and without a vapor barrier?

Aluminum foil insulation with a vapor barrier is designed to prevent moisture from passing through, which is crucial in humid environments to prevent condensation and mold growth. The vapor barrier is a layer that acts as a moisture control, enhancing the insulation's effectiveness. On the other hand, aluminum foil without a vapor barrier does not have this moisture-resistant layer, making it less effective in controlling moisture and potentially leading to condensation issues. The presence of a vapor barrier can also impact the thermal performance and energy efficiency of the insulation.