A sealed insulating tank having a tank wall fixed on a supporting structure, in which the tank wall has a multilayer structure which comprises, successively, a primary sealing membrane intended to be in contact with a product contained in the tank, a primary insulating barrier, a secondary sealing membrane, and a secondary insulating barrier, in which the secondary insulating barrier, the secondary sealing membrane, and the primary insulating barrier essentially consist of a set of prefabricated panels fixed on the supporting structure, each prefabricated panel comprising, successively, a rigid base board, a first layer of thermal insulation carried by the base board and forming, with the base board, an element of the secondary insulating barrier, a leaktight lining which completely covers the first layer of thermal insulation, being glued to the first layer of thermal insulation, and which forms an element of the secondary sealing membrane, a second layer of thermal insulation which covers a central zone of the first layer and of the leaktight lining, and a rigid cover board covering the second layer of thermal insulation and forming, with the second layer of thermal insulation, an element of the primary insulating barrier, in which the base board, the first layer of thermal insulation and the leaktight lining of the prefabricated panel have a first rectangular contour, whilst the second layer of thermal insulation and the cover board have a second rectangular contour with smaller dimensions than the first rectangular contour, with the result that the second layer of thermal insulation and the cover board do not cover an edge zone of the leaktight lining along the four edges of the first rectangular contour, and in which the prefabricated panels are juxtaposed on the supporting structure, parallel to one another, so that the edge zone of the leaktight lining of a first prefabricated panel each time adjoins the edge zone of the leaktight lining of a second prefabricated panel, the wall of the tank furthermore has sealing strips made from a flexible composite laminate material comprising at least one metal sheet bound to at least one fibrous layer, the sealing strips being arranged so that they overlap the adjoining edge zones of the leaktight linings of the prefabricated panels and glued leaktightly to the leaktight linings of the prefabricated panels in order to complete the secondary sealing membrane between the prefabricated panels, the wall of the tank furthermore has insulating blocks arranged on the sealing strips, an insulating block being each time arranged between the second layers of thermal insulation of two adjoining prefabricated panels so as to complete the primary insulating barrier between the two prefabricated panels, the insulating block having a layer of thermal insulation covered with a rigid board, with the result that the rigid boards of the insulating blocks and the cover boards of the prefabricated panels form a substantially continuous wall capable of supporting the primary sealing membrane, in which the insulating block has a reinforcing mat comprising a layer of fibers, the reinforcing mat being glued to the layer of thermal insulation on a face of the layer of thermal insulation opposite the rigid board, the insulating block being each time fixed to the prefabricated panels by gluing the reinforcing mat to the underlying sealing strip, characterized in that the reinforcing mat consists of a composite laminate material comprising at least one metal sheet sandwiched between two layers of glass fibers bound together by a polymeric resin, and in that the reinforcing mat has a stiffness under tension which is greater than or equal to the stiffness under tension of the sealing strips.