What is a key characteristic of a metal-clad structure?

A key characteristic of a metal-clad structure is that it has sides or a roof covered with metal. This metal cladding serves multiple purposes, including providing a robust barrier against environmental elements, enhancing fire resistance, and offering improved durability. Additionally, the metal can also contribute to the building's aesthetic appeal. In terms of lightning protection, a metal-clad structure can help establish a continuous conductive path for electrical currents, significantly reducing the risk of damage from lightning strikes.

This features contrasts with the other options provided, which do not fit the definition of a metal-clad structure. An open roof design suggests an absence of coverage, low durability materials imply a focus on weaker construction, and insulation with non-conductive materials does not align with the primary characteristic of metal cladding. Thus, the choice emphasizing metal coverage is clearly the most relevant in this context.