A lot of heavy metal, though there is a fair bit of not so heavy plastic in cars these days too.
Back in my 'early to mid life' working days I was very involved in the introduction of plastic components into the automotive world. I even presented technical papers on the subject. I was an expert! Back in those days it was all 35mm slides, and graphs drawn with flexicurves. We've come a long way since then. I should add I have done a fair bit of PowerPoint poisoning in my time too.
Struggling a bit for a blip today as you can see :-)