For the Lightweighting World Magazine, Mayflower Consulting summarized a study on roof materials to reduce vehicle weight. The article provides insight on the study, how it was formed, and some gaps that would make it more complete. Example, extrusions can be used to reduce the weight of a roof, yet because there are no extruders in the study group, this technology was omitted.

Light Duty Vehicle Market
A Look at 2017 Safety Component and Options for Future Lightweighting
Faced with pressing Corporate Average Fuel Economy (CAFE) 2025 targets, automobile manufacturers are using a number of methods to improve fuel economy. Engine downsizing, turbo