A big component of sustainable design is the facade or skin of the building. The analogy of skin is 2 fold and I will focus on aesthetics and porosity.
The facade like skin, is the first thing people see on a building. Wrongfully, many people judge whether they like a building or not by what the facade shows them. People have biases and first impressions are lasting.
The porosity of a facade plays a large role in its energy efficiency too. The skin on the body is semi-permeable and has numerous functions, and in sustainable design, there is a huge emphasis on energy retention. The more heat a building releases or needs to be inhabitable, the less sustainable the design.
The bones of the building are the structure that connects all of its elements. Often, bones are a means to an end, but in sustainable building practices, the structure can be expressed as architectural details.