Internal turbomachine casing having improved thermal insulation

Internal casing ferrule for a turbomachine, the ferrule being centred on a longitudinal central axis, wherein the internal casing ferrule includes:

• a main body, that is centred on the longitudinal central axis, that includes two longitudinal ends and that is delimited by a radially internal surface and a radially external surface relative to the longitudinal central axis;
• a thermal insulation envelope, that includes:
• a lateral covering portion entirely covering the longitudinal ends of the main body;
• along a section transversal to the longitudinal central axis, an exterior covering portion entirely covering the radially external surface of the main body;
• along a section transversal to the longitudinal central axis, an interior covering portion entirely covering the radially internal surface of the main body;
• the lateral portion connecting the interior and exterior portions;
• and
• a protective envelope, that at least partially covers the thermal insulation envelope and that includes, along a section transversal to the longitudinal central axis:
• a radially external protective portion at least partially covering the exterior covering portion;
• and
• a radially internal protective portion at least partially covering the interior covering portion;
• and wherein the thermal insulation envelope has a porous structure with a volumetric porosity greater than or equal to 50%.