A heat-transfer label assembly and method of using the same. In one embodiment, the assembly is particularly well-suited for decorating flexible plastic articles and comprises a paper substrate overcoated with a layer of polyethylene, a skim coat of wax overcoated onto the polyethylene layer, and one or more spaced apart, heat-transfer labels printed onto the skim coat. Each label is bondable to the article when activated by heat and consists of one or more ink design layers, each ink design layer comprising a mixture of polyester resins, a pigment, a cross-linking resin and a catalyst. When initiated by label transfer, the catalyst causes the cross-linking resin to partially cross-link the polyester resin to an extent that the label is endowed with protective properties while still retaining sufficient flexibility to avoid cracking when the article is flexed.