A vapor-barrier stop pre-treated piping insulation system including an insulation segment, a vapor-barrier stop, and a sealant. The insulation segment includes a cylindrical exterior surface, a cylindrical exterior surface, a first end surface, a second end surface, at least two ledge surfaces, and a wall extending between the cylindrical exterior surface and the cylindrical interior surface. The vapor-barrier stop is applied prior to installation of the insulation segment and extends, starting from at least the first end surface, over the cylindrical interior surface, the cylindrical exterior surface, the at least two ledge surfaces, and the first end surface along the insulation segment towards the second end surface. The vapor-barrier stop is configured to impede vapor-exchange through the vapor-barrier stop.