[Hehe]

I'm no engineer, but from my exp. of dealing with computer cooling, it's mainly ventilation.

Insulation only retards the timing of a place getting hot. However, the heat would build up eventually and you need to make way for heat to dissipate. If not, insulation actually works against you as it retains the heat for longer.

Open your windows, turn on some fan to move the hot air out. There's a reason why high-performance computer cases have holes everywhere for one to put fans on. Fans basically force the hot air out much more quickly allowing a lower temperature in the case.