Here's a brief description:
The Targus HeatDefense™ for Laptops serves as a barrier that shields your office furniture and lap from high heat generated by laptops. A crystalline compound absorbs heat by turning into a soft gel, keeping the laptop running cool to help prolong battery life. Once the heat is removed, the gel turns back into crystals and is ready for use again. No fans or power are required to operate which provides a highly portable, quiet laptop cooling solution.So, does this passive cooling method actually work? As long as you have a laptop that doesn't get too hot, the Targus HeatDefense is a reasonable option. It doesn't cool your laptop as effectively as active cooling mats that use fans, but the HeatDefense will keep your legs cool if you like to place your computer on your lap. I was able to compute for several hours using my ThinkPad X200 Tablet PC on my lap and my legs did not get warm one bit. The bottom of my ThinkPad got a bit warm, but the cooling pad did a nice job dissipating the heat and insulating my legs from the heat. I tested the HeatDefense with a few other laptops, and I experienced similar results. I was also running SpeedFan so that I could measure temperatures and I found that the HeatDefense pad was doing a nice job keeping everything fairly cool.
I generally prefer active cooling pads that use fans because I'm always trying to achieve maximum cooling, but the HeatDefense is very portable, so it's great for travel. I plan to keep one in my laptop bag when I know I'll be working with my notebook on my lap. If you're thinking about buying one, don't pay full price. You can get these on Amazon for a great price. Targus AWE45US HeatDefense for Laptops (Gray/Black)