In this article a case study the design of a plastic transport box is presented. After a short listing of the requirements, and explaining what is expected as definition of the product after the designing work, we formulate general assumptions about the environment of the product. We use the X-development method. We follow in parallel the twice left branches of the X, performing two key choices, the first one about the material and the second one about the optimized shapes. The X-development method permits the usage of environmental impact indicators during the design process, before taking important decisions. The targeted consequence is the reduction of the iterations during the design, especially in a LCA.