Panzer = armor, i.e. an ice crust formed on the inside of your igloo/shelter. But you probably need to fire up your "stove-of-the-week" for that to happen. Unlike in a tent, it is physically impossible to get toasty temperatures inside a snow cave or igloo - the extra energy is used to thaw the interior walls and ceeling. Which will re-freeze when you remove the heat source.

The point is: Watch out for ventilation in a snow cave/igloo.