Hexamine is a chemical crystal in the Formalin group. It is toxic, so take care not to breath in the fumes in a confined space. Esbit fuel is hexamine. There is some anecdotal evidence it may be of better quality. Both are very stable. They can dissolve in contact with moisture, but the packaging usually precludes this problem. Hexamine burns more evenly if broken up and fed gradually. Otherwise it tends to leave a great deal of black unburned residue on the cooking container. Niether would be my first choice for an emergency fire tinder. Trioxane is your other alternative. It is much more susceptable to evaporation if the packaging is opened and degradation over time. If you are using any of the small Esbit or homemade pocket stoves, a windscreen and pot lid are essential for efficient use.