Final answer:
Foam board has the least moisture permeability among the insulation options provided, due to its low thermal conductivity and design to minimize moisture transfer.
Step-by-step explanation:
The question at hand addresses the moisture permeability of different types of insulation. Based on properties of insulation materials, the type of insulation with the least moisture permeability is likely to be foam board. This is because materials like foam board, specifically polystyrene foam or Styrofoam, showcase very low thermal conductivity, which correlates with their effectiveness in minimizing both heat transfer and moisture penetration. Reflective foil, while capable of reflecting radiant heat, does not inherently have low moisture permeability. Fiberglass, while a very good insulator due to its high air content and low thermal conductivity, does not specifically target moisture permeability.
It is important to note that a material's R factor, which is influenced by both thickness (d) and thermal conductivity (k), is crucial in determining its insulation ability. However, the R factor primarily addresses heat transfer and does not account for moisture permeability directly. Materials designed for insulation such as foam boards are engineered to prevent moisture from passing through, making them ideal for applications where moisture control is essential.