24V cheap Chinese soldering iron heating element, get the ones with 4 wires (2 are for the heat sensor), you can slip inside a borosilic glass tube if needed or just tie around the outside of something.
Give it 24V and it gets hot VERY quick, give it 12V and it gets hot quick, give it 9V and it still gets hot but managing the tempreture at 9V is easier, great for small amounts of space or liquid, I use them alot for boiling tube heaters but I slip mine inside glass made to take heat then put that inside the boiling tube