Proper lumbar support is a necessary and fundamental requirement for any well-designed chair. Objective techniques to assess chair comfort necessitate the use of a sensing layer that may change the fundamental characteristics of the chair itself depending on its structure and materials. Other methods have attached equipment to subjects, which may influence their normal sitting behavior. In this study, I utilize new 3D body scanning technology to examine the person-chair interaction in flexible, material back chairs without adding anything to either the chair or the subject. I attempt to develop a new objective measure, volumetric deformation, which assesses the reaction of a flexible, material chair back to a seated user. In addition, this study aims to understand the relationships between perceived chair back comfort, objective volumetric deformation, subject anthropometric attributes, and ratings of perceived chair attribute comfort. Total chair back deformation is found to be significantly related to some subject anthropometric attributes, which provides further evidence that deformation is a useful objective measure for assessment of the chair back. Perceived overall back comfort is significantly associated to the perceived comfort of the lumbar support but not to any of the anthropometric measurements taken. The relationship between chair back deformation and pressure distribution should be explored in future studies.