In this paper, a methodology using Ashby plots is presented to select a thermoplasticpolymer to manufacture by thermoforming a dental aligner for orthodontics treatment. Thirteenbiomedical commercial polymers were selected and according to hierarchical criteria ofmechanical-geometric properties the comparison plots were done. The selected properties weretranslucency, water absorption, elastic modulus, thickness change during thermoforming andoriginal thickness of commercial polymer. According with orthodontists, the Ashby plots werestated as a fundamental support for the selection of the polymer since these properties directlyinfluence the design of the aligner.