Cattail leaf mats respond to humidity, sealing when wet and venting when dry

Evidence

The cattails have made a superb material for shelter in leaves that are long, water repellent, and packed with closed-cell foam for insulation. In the old times, fine mats of cattail leaves were sewn or twined to sheathe a summer wigwam. In dry weather, the leaves shrink apart from one another and let the breeze waft between them for ventilation. When the rains come, they swell and close the gap, making the mat waterproof. — Robin Wall Kimmerer, Braiding Sweetgrass, 822

Categorization

• XREF: Directly bridges ch45 ‘taking only given energy’ and the harvest ethic — a material is ‘given’ by plant adaptations that meet human shelter needs.