Inflating a rubber balloon leads to a dramatic shape change:​ a property that is exploited in the design of deployable structures and soft robots. On the one hand, inflation can be used to transform seemingly flat shapes into shelters, field hospitals, and space modules. On the other hand, fluid-driven actuators capable of complex motion can power highly adaptive and inherently safe soft robots. In both cases, just like the simple balloon, only one input is required to achieve the desired deformation. This simplicity, however, brings strict limitations:​ deployable structures need continuous supply of pressure to remain upright and soft actuators are restricted to uni-modal and slow deformation.

In this dissertation, I embrace multistability as a paradigm to improve the functionality of inflatable systems. In particular, I take inspiration from elastic instabilities arising from simple geometric principles---such as folding a 2D sheet of paper or snapping a curved cap to its inverse shape---to design balloons engineered to have a multi-welled energy landscape.

In the first part of this dissertation, I draw inspiration from origami to design multistable and inflatable structures at the meter scale. First, I propose a systematic way of building bistable origami shapes with two compatible and closed configurations. Then, using experiments and numerical analyses, I demonstrate that under certain conditions, pneumatic inflation can be used to navigate between the stable states. Finally, I combine the simple shapes to build large-scale functional structures such as shelters and archways. Because these deployable systems are multistable, pressure can be disconnected when they are fully expanded.

In the second part, I again use origami as a platform to create soft actuators capable of multimodal and arbitrary deformations based on a single pressure input. I start by focusing on the classic Kresling origami:​ a pattern that once folded, takes on the shape of a faceted cylinder that simply extends, contracts, and twists upon inflation and deflation. By modifying one of the facets, I show that the module can become bistable, i.e. the modified facet snaps at a certain pressure threshold. This snap-through instability breaks the rotational symmetry and unlocks bending as a deformation mode upon subsequent deflation. By combining multiple of these modified Kresling cylinders---each one snapping at different pressure levels---I then build actuators that deform along vastly different trajectories from one single source of pressure. Guided by experiments and numerical analyses, I inverse design actuators with prescribed deformation modes to demonstrate their potential for robotic applications.

Finally, I exploit snapping instabilities to decouple the input signal from the output deformation in soft actuators. In particular, I design a soft machine capable of jumping based on the snapping of spherical shells. As this instability is accompanied with the sudden release of energy at constant volume, i.e. no influx of fluid is needed to trigger the large deformation, the robot jumps upon an arbitrarily slow volume input. Using experiment and numerical simulations, I optimize the actuator's release of energy and jumping height.