A new class of Lab-developed “field-responsive mechanical metamaterials” (FRMMs) employ a viscous, magnetically responsive fluid that is manually injected into the hollow struts and beams of 3D-printed lattices. The fluid’s ferromagnetic particles located in the core of the beams form chains in response to the magnetic field, which rapidly stiffens the fluid and the lattice structure. Photos by Julie Mancini/LLNL