Perhaps it’s the lack of gas struts, but the 4C’s rear hatch is one heavy boi. It takes both arms to lift it up, but keeping it up to position the prop rod is easy as long as you’re not holding anything else.
This becomes a real problem when you don’t want to drop your groceries on the floor, but that use case has occurred only once for me.
So what’s it made of...a panel of glass which is heavy for sure, plus a beefy frame to support that glass. Attached to all that is the boot cover, which is just SMC. The plastic engine cover has the only “4C” badge visible from outside.
The 4C Spider loses the rear glass, which means its lid is probably lighter.