It keeps you cool
It does feel very cool when you lie on it and that lasts for quite a while.  Usually I fall asleep long before the cooling has ebbed but during the night when I awake it is not cool at all so I am guessing about an hour to two.  The only really effective way to use this is to get two pillow pads and swap them out when you wake and the first will cool down while you are using the second.  If you are an all night sleeper who doesn't wake then I am not sure this would be the best alternative for you.  But keep in mind NOTHING stays cool the entire night.
Rating: 5 stars