Fat present below the skin surface in our body, acts as a barrier against

Subcutaneous (hypodermal) adipose tissue functions primarily as an insulating layer that reduces heat transfer from the body to the environment. Clinical and anatomical sources note that subcutaneous fat conducts heat poorly and forms an insulating barrier that decreases loss of body heat, helping maintain core temperature [1]. While the skin as an organ provides multiple protective roles (e.g., limiting fluid loss and blocking pathogens), the fat layer beneath the dermis is mainly responsible for thermal insulation rather than directly preventing loss of salts, essential body fluids, or microbial entry. Therefore, the best answer is prevention of loss of heat from the body [1].

Sources

1. [1] https://www.ncbi.nlm.nih.gov/books/NBK499843/