  In this paper, we introduce the concept of 2-way 2-fold genus-1 non-woven
fabrics that can be used to design self-regulating breathable building skins.
The advantage of non-woven structures over woven structures for breathable skin
design is that they can completely be closed to stop air exchange. We have
developed a theoretical framework for such non-woven structures starting from
the mathematical theory of biaxial 2-fold Genus-1 woven fabrics. By
re-purposing a mathematical notation that is used to describe 2-fold 2-way
2-fold genus-1 woven fabrics, we identify and classify non-woven fabrics.
Within this classification, we have identified a special subset that
corresponds to satin woven fabrics and allows for maximum air exchange. Any
other subset of non-woven structures that correspond to other classical 2-way
2-fold genus-1 fabrics, such as plain or twill, will allow for less air
exchange. We also show that there exists another subset of satin non-woven
fabrics that can provide the biggest openings.
