[davee5]

This is why at Apple the division making MacBooks is called "portables" and not "laptops." They're officially not supposed to go on your lap.

Also the thermal limits of the human dermis are pretty well studied and documented. The vast majority of CE products are designed not to exceed 50°C, which is when the thin skinned (children and elderly) start to get second degree burns pretty fast. 60°C is where you burn almost immediately.

Interestingly 45°C is "threshold of pain" for most folks, but few companies set that as the target limit. Since thermal dissipation is a ∆T game that last 5 degrees matters a LOT for wattage out (on a hot day outside 30-35°C is a good surface temp estimate, so that last five degrees is the difference between 10 or 15 degrees out, a non trivial delta.)