Which layer of skin is mainly composed of fat and serves as insulation?

The layer of skin that is mainly composed of fat and serves as insulation is the subcutaneous layer, also known as the hypodermis. This layer is situated beneath the dermis and is primarily made up of adipose tissue, which functions to provide thermal insulation for the body, helping to maintain body temperature. Additionally, the subcutaneous layer acts as an energy reserve and provides cushioning to protect underlying structures such as muscles and bones. It also plays a crucial role in anchoring the skin to the underlying tissues while allowing some degree of flexibility and movement.

The epidermis is the outermost layer of skin and is mainly composed of keratinized cells that provide a protective barrier. This layer does not contain fat and is not involved in insulation. The dermis lies beneath the epidermis and contains connective tissue, blood vessels, and nerve endings, serving functions related to sensation, support, and nourishment but does not primarily function for insulation as the subcutaneous layer does. Therefore, the subcutaneous layer is the correct answer for its specific role in insulation and fat storage.