In many product areas, a growing trend can be observed towards variant design, i.e. the development of customized designs based on variations of mature product models. We have developed a Virtual-Reality (VR) system for variant design that supports the real-time scaling and subsequent simulated assembly of hierarchical, CSG-like parts. An XML-based format, VPML, serves as description for the scalable CSG parts. VPML part descriptions determine how the scaling behavior of the whole part affects the scaling of its subparts, constrain the translation and rotation of subparts w.r.t. their parent parts, and define the scalable parts’ dynamic mating properties. The part descriptions are utilized by several submodules of the overall VR system including: a) algorithms for real-time CSG visualization, b), the updating of part geometry using the ACIS CAD kernel, and c), the assembly simulation engine. The VR system runs in a CAVE-like large screen installation and enables interactive variant d...