Shape morphing with expanding foam drops

Polyurethane foams find extensive application in a wide range of industries due to their remarkable thermal properties and structural resilience. These foams can expand many times their original volume during curing, making them ideal for lightweight casting and backfilling. We investigate how expanding foams with free surfaces can be used to create 3D forms from quasi-2D molds. In our experiments, we drill an array of shallow wells of different sizes and fill them by pouring uncured reactive liquid foam. The expanding foam overflows out of the wells and forms a domed drop shape. We model the final foam shape using a quasi-static drop approximation based on the balance between surface tension and gravity. We explore various configurations, including colliding foam droplets and make progress toward solving the inverse design problem. By understanding the connections between foam expansion and well morphologies, we work toward developing a novel strategy for shape morphing that offers an alternative to classical 3D printing.