C-4 burned fast and hot, like a little jet. It didn't smoke. Period. I heated water but never C Rats, due to either burning, on the bottom or heat expansion pushing out stuff like spaghetti, like a huge toothpaste. I used a certain size to boil water for cocoa or LRRPS, and heat tabs for everything else. I had quite a battery of recipes to alter things like pork slices or beef slices (with juices) or a pecan cake roll. And of course Peaches and Pound cake. Our C-4 was in a longer strip-like rather than a block like the photo. It had a strip of green sticky covered withtape along one side. C4 was GREAT stuff.