Last week's discussion of chill mats for laptops prompted some excited discussion and raised some interesting ideas. One emailer suggested using two books for a cheap improvised alternative; another suggested mats were entirely unnecessary, which I suspect means they've never visited central Australia in the summer. But just how much difference do they make? Reader Carl did some testing of his own and got some interesting results, as he explains in an email: "An air gap with ventilation taking heat away from the casing is the key. I use an external monitor and keyboard at my office, and so I've got more freedom to play around with positioning. Using Speedfan to watch CPU/GPU/core idle temperatures (and having measured normal performance) I've tried the following:
(1) propping it vertically with an air gap behind: this runs about 2 degrees cooler than benchmark. This saves surface area but port/fan placement makes this tricky and/or restrictive, and some orientations actually cause it to heat up;
(2) sitting it flat/flush on the top of cool metal shelving to see if that would work as a heat sink (negligible difference from 1);
(3) like (2) but raised on for 1-3cm 'footstands' made from stacked pieces of mousepad foam: this ran 3-4 degrees better than benchmark;
(4) like (3) but with a regular standing fan blowing in its general direction from across the room, and a folded sheet of tinfoil wedged between the handrest (which heats up) and the closed screen, protruding to catch the air and act as a radiator (okay, I was bored!): 6-10 degrees better than benchmark. I have no idea if the tinfoil radiator is better than having the lid open but just by touch it's definitely drawing off at least some heat from the hand rest.
Basic, obvious-in-hindsight findings: best to be sure that the built-in fan's exhaust is blowing clear and not blocked off or recirculating, and maximise the surface area ventilated by cool air. Oh yeah, and CPU intensive screensavers can undo all your work!"
If you've done your own experiments with cooling techniques, let's hear what worked for you in the comments.