Tubular textile insert for strengthening material

Tubular textile inserts to strengthen material, made up of a stock of successive layers of contiguous parallel threads linked together, comprising:

• a first single-direction cylindrical layer (27) defining a central axis and formed from several contiguous parallel threads arranged in a spiral in relation to the central axis, the spiral arrangement defining a first pitch;
• at least a second single-dash direction cylindrical layer (32), also formed from several contiguous parallel threads arranged in a spiral but at a pitch disposed in a direction opposite to the first pitch;
• the two layers cooperatively defining a generally cylindrical plane, the cylindrical plane containing a plurality of generating lines, each generating line is angularly spaced apart from adjacent generating lines and extends generally parallel to the central axis;
• several binding threads (18), arranged parallel to the generating lines of the cylindrical plane, to link together the threads of the first and the second layers, said binding threads interlocking said layers by forming knit loops encompassing said layers in a manner to allow movement of one of the layers with respect to the other layer.