The textile industry views fibres as natural or synthetic filament, such as cotton or nylon, capable of being spun into yarn, or simply as material made of such filaments. The discovery and rapid evolution of nanofibers have led to a vastly improved understanding of nanotechnology. For heat flow analysis of wet porous nanostructure fabrics, the liquid is water and the gas is air. This book is intended to be essentially a practical guide; a detailed discussion of the theoretical side of the subject should be outside its scope. A considerable literature exists and the reader who wishes to make a further study of this aspect of the subject is referred to the bibliography at the end of this book. However, for a proper appreciation of what is involved to heat flow in porous nanostructure fabrics, certain basic theories and concepts should be understood.