Is the crystal coffin vacuum?

Crystal coffin is a coffin made of crystal glass, and its composition is mainly pure silicon dioxide. Crystal coffins are very expensive and complicated, and are generally used to preserve the remains of important figures such as politicians.

In order to preserve the body for a long time, most crystal coffins are filled with inert gas, such as helium. The crystal coffin is evacuated every once in a while to keep the pressure balance in the coffin.