This paper presents a new product design approach based on a unified set of Design for eXcellence (DFX) guidelines applied to the design of sustainable mass-customized products. In order to gather the main product design requirements for developing a sustainable mass-customized product, an integrated product design process guideline is introduced to go beyond conventional engineering product requirements and consider new sustainable and mass-customization ones. The integrated product design process guideline proposed takes into account all product lifecycle phases in order to assess and identify all possible impacts of product design decisions in further lifecycle phases.