havesomeseichel-
can you inform me about what is “excessive”?
I wish I had hard-and-fast numbers, but I don’t (sorry). The pretty-much-useless answer is: hot enough to damage your PC’s components.
What kind of surface material is best to place your laptop on to prevent overheating?
Worst – soft, that the PC can sink in to and block ventilation holes.
Better – hard, so the vents are unobstructed and a little air gets under the PC.
Good – Raising the PC for additional under-the-case ventilation (as “veyatziv” and “YW Moderator-72” have done).
Best – a under-the-case appliance that has fans for additional cooling. Google “laptop cooling pad”. I don’t have any firsthand knowledge of specific pads.