Abstract: A heat transfer comprising a temporary support and a label carried on the support. The label comprises a layer of a polyurethane resin system which includes a polyurethane obtained by reaction of a diphenyl isocyanate, a free glycol and a polyester either of the formula ##STR1## wherein R is an alkylene radical of 2 to 8 carbon atoms and R.sup.1 is an alkylene radical of 4 to 10 carbon atoms or of the formula ##STR2## wherein R.sup.11 is an alkylene radical of 4 to 8 carbon atoms. The polyurethane resin system further includes a cross-linking agent and a catalyst so that when the label is placed in contact with an article to be marked and subjected to heat and pressure, the resin system is converted to an inert insoluble and wear resistant form and a substantially permanent marking is produced on the article.