The cup fits snugly on top, sealing the chimney effect.
Only a few mins 5-10, for a cuppa to be ready. Lighting the cardboard and letting it 'volcano' first then popping on the bottle or cup.
The burner certainly 'volcanoes' well, you can almost see wood gas effects, the gas would ignite if a match was held to it. Blowing in the lower hole shoots the flame up a few inches more.
Even though it was 3degs, the dog was happy watching/snoozing !
The cup, big enough for pasta/pot noodle for one, fits snugly into the side rack while the bottle is on. Note the cork upside down to avoid it blasting off, the bottle can be turned by the handle that supports the cup when it's boiling. This prevents the fire falling out.