The simplest laptop cooling devices are ones that require no moving parts or external power.
We put eight laptop cooling devices to the test, and among the passive, or unpowered, devices we tested, we were particularly impressed by [...] a massive chunk of ABS composite (the same stuff used for Lego bricks and plumbing pipes), that looked like a cutting board with a big "X" on it. A more inelegant computer accessory would be hard to find, but the [winner] was inexpensive, could handle large laptops, and was just as effective as our fan-equipped laptop coolers.