Product Design is at the core of engineering, and is often transdisciplinary. Holistic product models and viewpoints are needed for making early design decisions. Such models must place the product in its relevant, dynamic environment, thus taking into account societal factors in addition to engineering disciplines. System Dynamics (SD) can apprehend semi-qualitative societal variables. It also has the advantage of transparency, and demonstrates the essential qualitative dynamics of large complex systems. Several SD model types and fragments (“molecules”) have been successfully used around product development, but their integration is unclear. We integrate several SD molecules to form a simple, yet holistic model for product design. It is based on the Bass diffusion model; the main novelty is combining this with customer preferences. External-facing product functions contribute to utility, backed by internal functions. It proposes an expression for part-utilities, and distinguishes between types of network effects. The model structure is generalizable to products, services, and wider ecosystems. It systematizes data acquisition by showing gaps for input by e.g. conjoint analysis, and allows value-of-information calculations. We demonstrate the model structure using the introduction of the household freezer. Product success is dominated by successive SD regimes: initially technological improvement, modulated by a niche and durable goods replacement rate, then by network effects. The next step is better quantifying the more difficult factors, giving standardized ranges of values & functions, based on compiled empirical data across a range of products. This research furthers SD “molecules”, aiming to clarify the “basic physics” of product design & adoption.