Every living being depends on certain ambient temperatures and requires a specific preferred temperature for the activity of its bodily functions. In this context, the "second skin" plays a significant role. Whether it is the fur of mammals, the feathers of birds, or the clothing and building envelope of humans – thermal insulation has an important survival function. Throughout history, humans have looked to nature for inspiration in the invention of warming clothing and the thermal insulation of buildings. The ninth volume of our non-fiction series under the motto "Ask Nature" vividly illustrates important principles of thermal insulation from the animal kingdom and their application in human technology. Physical and technical fundamentals help the reader understand the principles of thermal insulation. Methods, construction instructions, and simple experiments enable self-directed learning.