A flat cardboard blank forms tubular envelope type packaging for a pack of jars. The blank extends substantially along a plane formed by a longitudinal axis and a transverse axis perpendicular to the longitudinal axis, where the plane further defines a packaging axis substantially perpendicular to the plane. The blank includes: tubular-blank panels including at least one top panel, two lateral panels, a base panel, a unit for securely attaching for closing the expanded blank on itself; cut lines, slot lines and score lines between the tubular-blank panels for folding the tubular-blank panels, expanding the blank and shaping the packaging of the pack; and a spacing/bracing part connected to the tubular-blank panels by cut lines, detachable from the tubular-blank panels when the packaging of the pack is shaped for being arranged and expanded into the bracing spacer and forming bracing walls of the braced jars on the lateral walls.