Which insulation type is known for filling gaps and cracks effectively?

Spray-on insulation is particularly effective for filling gaps and cracks due to its ability to expand and conform to irregular surfaces. When applied, spray-on insulation typically comes in a liquid form and quickly expands as it dries, allowing it to seep into small spaces and create a tight seal. This characteristic is crucial for preventing air leaks and ensuring energy efficiency in buildings.

In contrast, cellulose insulation, while effective for insulation, tends to settle over time, which may leave gaps. Fiberglass batting is designed for larger spaces and is not as versatile for intricate openings. Foam board insulation, although it provides a solid layer of thermal resistance, is rigid and does not adapt well to small cracks and gaps. Thus, spray-on insulation stands out as the optimal choice for ensuring a comprehensive seal around obstacles and within irregular spaces.