I purchased this item in hope that it would extend the battery life of my laptop, whilst keeping it cooler.
The mat is filled with a crystalline material, which feels very much like rock salt crystals through the cover. These crystals draw the heat away from the laptop and into the mat and whilst doing so, become softer. Eventually at their hottest, the crystals seem to become liquid, at which point they can no longer offer any cooling ability.
I have a high end Dell XPS 16, which gets very hot when running.
I have noticed an improvement in battery duration whilst using the mat. The fans take longer to come on and run for shorter periods.
However, once the mat has expended its cooling ability, the crystals in liquid form stay very hot. If left in contact with the hot running laptop, this only makes things hotter. Once the crystals have become liquid it is necessary to remove from the laptop.
In my experience this usually takes somewhere between 2.5 - 4 hours, depending on what you are running on your laptop.
I purchased 2 of these mats, one for me and one for my wife. My wife uses her laptop much less frequently, so if available I swap the expended mat for the other mat.
I have not needed to swap back to the first mat again, but I think it takes longer to cool and return to a usable condition. I would guess 4+ hours.
As the crystals become liquid, be sure to leave flat when cooling, or you will find the crystals pool to the lower section of the mat, when cool.
Many other reviews have mentioned slipping. I concur with this opinion. My laptop is large, heavy and has rubber feet to prevent slipping. The material on the side of the mat you place the laptop on, appears to be some kind of Nylon, or Polyester. Similar to a suitcase lining, or tent material. This material is VERY low friction and added to the profile of the mat surface (peaks and troughs to allow convection to move hot air around), this offers very little resistance to the laptop slipping.
I have found that even minimal movements can cause the laptop to begin to slip.
To this end, I find that the mats are not best suited to use on the lap. If used beneath the laptop on a fixed surface, such as desk, or table, etc. There is much less risk of slipping.
The additional complication I have with my laptop, is the 9 cell battery. This protrudes from the bottom of the laptop along the rear bottom edge (imagine 5 x AA batteries end to end, forming a long cylinder attached to the body of the laptop). This raised the laptop a little when on a flat surface, which is generally no bad thing.
However, this mat needs to be in contact with the base of the laptop, to be effective. With the back only raised, this restricts the amount of contact with the mat. I have tried different positions, some better than others, but it will not fit perfectly.
Regardless of this issue, it does still offer a benefit in cooling, just not as much as with a flat bottomed laptop.