The blue flame is composed of 3 layers, the outer layer is the dark translucent part that appears a darker blue. The inner layer, which is in lighter and opaque is next to the outer flame. In front of that opaque flame is the sweet spot or what you would be calling as the hottest spot. This inner flame can heat metal and burn any surface real fast. You have to be very careful in handling this product since it can be very dangerous especially when you are around children. And don’t forget to keep it in a safe place where children can’t reach it.