The horizontal heat transfer in the continuous casting of steel is exceedingly important since non-optimum heat transfer results in inferior surface quality of the product and process control problems. The horizontal heat transfer is controlled by both the thickness and the crystallinity of the solid slag film formed between the steel shell and the water-cooled, copper mould. This study is focused on the efficacy of thermal analysis techniques in measuring the fraction of glassy (or crystalline) phase present in the slag films. The glass fraction has been determined for several slag films using a variety of techniques. The results obtained are summarised and the problems encountered with thermal analytical techniques are outlined and discussed.