I just discovered something quite by accident. My magnetic work-lamp doesn't stick to the engine hood, nor to the 4 doors. That tells me the hood & doors are not made of steel. But they don't seem to be plastic. Are they aluminum? I doubt they'd be stainless steel, which also happens to be non-magnetic. Both AL or SS would be good. No rust. Yay! But the 4 fenders & roof & trunk lid are magnetic, so they're still made of steel.

I heard BMW doesn't use steel either for many of their body panels...forget what my friend called the material but it's a type of plastic I guess.

Hood, doors, and roof appear to be aluminum.

Due to EPA gas mileage increase ruling more and more companies are going to aluminum and higher strength steel to reduce weight and increase MPG. This is the future. My Corvette was aluminum chassis and fiberglass. My Maxima also has non steel components

It is, indeed, the future. Hopefully, Infiniti has at least begun to develop new combination materials. I am quite intrigued by the engineering advancements that make the car more rigid, quieter, larger, and faster, while dropping weight significantly. For instance, Cadillac has broken some ceilings for parts of the main frame of the new CT-6 full sized sedan. It is larger than an A-6, larger than a Merc E cvlass, about the size of the BMW 7-series, but weighs less than any of them. They were also able to design an AWD system that allows all of the torque to be sent to the front wheels if the back wheels have no grip. They used newly designed materials for rigidity and sound deadening on the body frame as well. I'm sure it will cost closer to a BMW 7 then an Infiniti Q70, but it will also out-perform both.
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https://www.youtube.com/watch?v=hRY95IjEsno