Abstract
Botanical nastic systems demonstrate non-directional structural responses to stimuli such as pressure, light, chemicals or temperature; hygronasty refers to systems that respond specifically to moisture. Many seed dispersal mechanisms such as wheat awns, legume pods, spruce and pinecones fall within this classification. The variety of behaviours varies greatly from opening and closing to self-digging, but the mechanism is based on differential hygroscopic swelling between two adjacent areas of tissue. We describe the application of hygronastic principles specifically within the framework of textiles via the lens of structural hierarchy. Two novel prototypes are presented. One is designed to increase its permeability to airflow in damp conditions and reduce permeability in the dry by 25-30%, a counterintuitive property compared to conventional cotton, wool and rayon textiles that decrease their permeability to airflow as their moisture content increases. The second prototype describes the design and development of a hygroscopic shape changing fibre capable of reducing its length in damp conditions by 40% when compared with dry.