The defining characteristic of a muffle furnace is that it separates the object to be heated
from all by products of combustion from the heat source. With modern electrical furnaces,
this means heat is applied to a chamber through induction or convection by a
high-temperature heating coil inside an insulated material. The insulating material
effectively acts as a muffle, preventing heat from escaping. A well-built muffle furnace
can reach extremely high temperatures with a high degree of uniformity and accuracy,
while preserving the purity of the chamber environment.