This paper presents a design framework for wearable electronic textiles. The focus is on the design and simulation issues that arise from the interaction of the electronic textile, the human body, and the environment. To assist in design choices within this framework, a simulation environment is described that uses Ptolemy II to integrate models of the physical environment, human locomotion, sensor behavior, network communication, power consumption, and software execution. We describe results for two e-textile design case studies, a shape-sensing garment and a wearable phased array of microphones, demonstrating how the design framework encompasses the effects of design variables for wearable electronic textiles.