What type of insulation is typically used for concrete foundations?

Rigid Polystyrene insulation is commonly used for concrete foundations due to its excellent thermal properties and moisture resistance. This type of insulation is ideal for below-grade applications, where it provides effective insulation against the cold ground. It tends to have a high compressive strength, which means it can withstand the weight of the concrete and the structure above it without losing its insulating capabilities. Furthermore, it does not absorb water, making it a durable choice for environments where moisture may be a concern, such as basements and foundation walls.

The other types of insulation mentioned have specific uses but are not typically chosen for concrete foundations. Fiberglass insulation, while effective in framed walls and ceilings, is not suitable for direct contact with concrete because it can absorb moisture, which leads to mold and insulation failure. Cellulose insulation is primarily used in attics and walls but is also not appropriate for direct exposure to concrete due to its vulnerability to moisture. Spray foam insulation is versatile but is generally more suitable for enclosed cavities and can be more expensive; it is less commonly used for foundations where rigid insulation is preferred for its ease of installation and flat surface.