Unfortunately I have not been in a chemistry class in 3 years and our system will depend on a efficient endothermic reaction. I am looking for some data on the best chemical reactions that will give us the most energy absorption per weight. Ideally it would also last for an extended period of time, as this will also be a deciding factor. This application will be used to cool people, so it will need to be safe. Also any reference where I could find the data on heat removal would be nice. The goal is to make cold packs that we can install in our system.