A stopper rod comprises a body (11) having a central passageway (12) with part of a carrier rod (13) fixed in the passageway and a further part outside of the passageway for attachment to a lifting device. An enlarged part of the passageway defines a sealing surface (14) and an insert (16) around the carrier rod is partly received in the enlarged part. Retention means (17, 18) are carried on the carrier rod and expandable means are disposed around the carrier rod between the insert (16) and the retention means (17, 18). The expandable means include an expandable graphitic composition formed by removing a proportion of interstitial water from an expandable graphite formulation. The insert has a co-efficient of thermal expansion no greater than that of the carrier rod whilst expansion of the expandable means is greater than that of the carrier rod.