Harvard researchers have turned regular knitting into a way to make smart fabrics that can shift between different shapes and perform functions like controlling lights or counting steps. Using stretchy yarns and industrial knitting methods, they created thick, flexible textiles that can naturally curl and lock into multiple stable forms. By adding conductive yarn, the team transformed these shape-shifting fabrics into soft, stretchable switches that can respond to movement and control electronic devices. The project was led by Kausalya Mahadevan, a recent Ph.D. graduate who is now a postdoctoral researcher in the lab of Katia Bertoldi, a professor of applied mechanics. Their findings were published in the journal Advanced Functional Materials. The team used highly elastic yarns and a technique called plating, which involves placing different types of yarn on opposite sides of the fabric. This created dense, thick textiles that naturally curl into three-dimensional shapes, similar to how the bottom of a cut T-shirt might curl upward. To create fabrics that can snap between different configurations and stay stable, the researchers arranged horizontal and vertical stripes in specific patterns. By studying how the fabric's structure and material properties influenced this snapping behavior, they identified the physical conditions that allow knitted textiles to be multistable. They also developed a way to simulate the behavior by treating the fabric as a continuous material rather than modeling each individual strand of yarn. The researchers then integrated thin conductive yarns into the fabric to demonstrate its potential for practical use. These conductive fibers turned the knitted structures into soft, stretchable switches that change their electrical state when the fabric shifts between configurations. In one experiment, a knitted shell was designed to turn an LED on and off as it moved between stable states. Another prototype was a wearable switch that could be placed over a knee or elbow, detecting movement and counting steps using an Arduino. A third example was a reconfigurable lamp shade with three switches, each controlling a different color of light as the fabric stretched and changed shape. The machines used in the research are similar to those found in industrial garment factories, which suggests that this technology could be scaled up for mass production. From a scientific standpoint, the work also brings textiles closer to the field of nonlinear mechanical metamaterials—engineered structures that can bend, buckle, and snap in controlled ways to achieve specific functions. The research was supported by several grants, including funding from the National Science Foundation and the Army Research Office.