We present a procedural approach to authoring layered, solid models. Using a simple scripting language, we define the internal structure of a volume from one or more input meshes. Modeling operators, which may include simulations or sculpting operations, are applied within the context of the language to shape and modify the model. Our framework treats simulation as a modeling operator rather than simply as a tool for animation, thereby suggesting a digm for modeling as well as a new level of abstraction for interacting with simulation environments. Capturing real-world effects with standard modeling techniques is extremely challenging. Our key contribution is a concise procedural approach for seamlessly building and modifying complex solid geometry. We demonstrate our language using a flexible tetrahedral representation. We show examples of our system interfacing with finite element and particle simulation tools to produce a variety of complex models.