Glow plug

The plug has a heating rod (3) movable in a housing (1) in an axial direction. The heating rod protrudes from the housing to a front end. A measuring membrane (4) and expansion measuring strips (6) are provided for measuring combustion chamber pressure that act on the heating rod. Heat guiding materials (7) are filled in a sealed housing inner space. The materials are changed from fluid consistency to pasty consistency, at temperature that is occurred during operation. The materials guide heat produced by the heating rod to the housing. Silicone oil is filled in a rear partial space.