"A warm sphere with a recessed button on top."
The strongest grenade in the Thermal family. Way more powerful than either MK I or MK II. It will set enemies ablaze for a long time and the player character should also be careful walking in the area where this grenade has been thrown as it might also make you get caught on fire too.
Enemies with high enough Heat resistance can be hard or impossible to set on fire.
Can be used as ammo for grenade launcher.