They look to me like they're cast with holes.
Also the holes are chamfered, which is actually the wearmark when they need replacing.
As far as hard usage goes, yes, I have had them pretty " warm " drivingin mountainous terrain.
I've done a LOT of research before I purchased them.
Many of the " cracked rotor horror stories " probably could have been avoided, if people had done their homework, as I did.