Purpose ‐ The aims of this article are to introduce a modularization framework and a method for the formation of modules. Design/methodology/approach ‐ A methodological framework is presented to guide designers and engineers in the formation and selection of suitable modules in developing customized products. Detailed explanations of the framework are presented theoretically. This framework interacts with different product development participants such as resources, customers' preferences, design architecture for planning, and scheduling a custom-built product. A new method is proposed with a case example to facilitate the formation of modules. Findings ‐ This paper investigates the potential of the modularization framework, usable for prioritizing the components dependencies and creating required number of modules. It also explains the overall concept, usability and rules/methods for the module formation applied to product design, to allow a greater degree of freedom for the designer, and the opportunity to reduce development time and increase customer satisfaction. A method, based on the rules for modularity concept is proposed within the scope of this paper. Research limitations/implications ‐ The framework and the method of modularization as illustrated in this article are based on a theoretical hypothesis. Both the approaches require implementing in a real industrial environment in order to generalize their effectiveness, applicability and consistency in the manufacturing arena. Practical implications ‐ Since product architecture is an important element in determining the value and flexibility of the product development process, the relationship pattern between the architecture and productivity is therefore worthy of careful investigation. The aims of modular framework and rules for modularity are to incorporate design variables and dependency structure with a view to enhancing product development lead time and will contribute to the exploitation of overall bottlenecks of manufacturing systems. Originality/value ‐ The implementation framework for modular product architecture seems unique as its potential value could be applied in the industrial environment for production flexibility and reducing bottlenecks. Along with the framework, the presented modularity rule or method will contribute to business architecture with a view to providing more reliable operation, easier maintenance and faster product development time.