A careful reading of all the published stuff on the R8 has failed to answer this question conclusively for me:
Is the R8 body ALL alloy?
Audi's published descriptions go on and on about the all alloy, mostly aluminum "ASF" and "body frame" with "aluminum panels", etc., etc.. But nowhere do I see specifically mentioned clearly what the exterior panels (fenders, door skins, "boot and bonnet" skins, roof skin etc.) are made of.
It's terribly "sexy" (in a car guy sort of way

) to say it's an "all aluminum" body, but (having owned at least part aluminum cars and sailed on aluminum boats) steel is really easier to live with as an outer skin.
So what is the R8 skin? Does your magnet stick to it, or not? (of course, that's the old test for lead...or bondo...filler, but one hopes there's no factory filler on the R8 like there was on so many Italian coach bodied cars in times past!

)