Futurelooks puts two passive laptop coolers, the Thermaltake iXoft and the Lapworks Futura, into a head to head battle.  Since they are fanless, both are silent, but which one actually cools?  Here's a clip:

If you take a peek at your local computer store (or online store), you’ll find that the options are plentiful. On the one hand, there are powered solutions that either plug into a USB port for juice or carry a set of batteries of their own. These are typically equipped with fans that blow cool air into the underside of your notebook, helping to keep the temperature down to a more comfortable level. These don’t do much in terms of keeping your thighs nice and chilled, but they’ll certainly serve up a cooler hard drive and a more efficient computer.

Source: Futurelooks