The development of variable-stiffness systems is key to the advance of compact engineering solutions in a number of applications spanning from exoskeleton to space structures. Rigidizable structures exhibit variable-stiffness based on external stimuli. This function is necessary for deployable structures, such as inflatable space antennas, where the deployed structure is semi-permanent. We design, analyze, and test a rigidizable structure based on inflatable octet-truss cells. An octet-truss is a lattice-like configuration of elements, traditionally beams, arranged in a geometry reminiscent of that of the FCC lattice found in many metals; namely, the truss elements are arranged to form a single interior octahedral cell surrounded by eight tetrahedral cells. Unlike traditional octet-truss designs, the elements of the system presented are pneumatic air muscles, also called McKibben actuators.