The key to Jetboil lies in an almost invisible ruffle of aluminum at the base of the heating cup. The Flux Ring. The job of the flux ring is to suck as much heat as possible from the flame and transfer it to the water. It's like the big heat sink on your computer's CPU, except in this case it isn't trying to cool things down.
Even with a flame going full blast you can put your fingers near the edge and feel only a little warmth, the rest of the heat is being efficiently dissipated into the cup and, most importantly, into the water. They claim over 80% efficiency.
What's happening is that the Flux Ring increases the surface area of the cup. With a traditional stove the pan bottoms are flat and there isn't much surface area the flame comes into contact with. With the Flux ring you get a huge surface area exposed to the flame and all of that heat is quickly transfered into the cup and into the water. The cup is made of aluminum (anodized) and is a very good conductor of heat.
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