Which of the following materials is commonly applied for insulation in residential buildings?

Fiberglass is commonly used as insulation in residential buildings due to its excellent thermal resistance properties, lightweight nature, and relatively low cost. It is made from fine strands of glass and is designed to trap air within its structure, which reduces heat transfer. This makes fiberglass insulation effective at maintaining comfortable indoor temperatures, improving energy efficiency, and balancing heating and cooling loads.

In contrast, steel, concrete, and brick, while they may have structural roles and some insulating properties, are not primarily designed or commonly used for insulation purposes. Steel can conduct heat, concrete has a higher thermal mass but is not effective as a standalone insulator, and brick is often used for wall construction but does not provide sufficient thermal insulation without additional insulating materials. Therefore, fiberglass stands out as a material specifically tailored for insulation in residential construction applications.