Ends of thermoplastic polymeric strap are joined together using a hot sealing blade of substantially rectangular transverse cross section and having corners with an effective radius in the range of about 0.005 inches to 0.03 inches. Joints or welds produced by this sealing blade have a novel configuration in which a fused interfacial region includes an annular mass defining at least one elongated cavity. At least two such cavities are present within the region and together span the width of the strap. Such welds are stronger than prior art welds, and can consistently be produced having a joint strength of at least about 85 percent of the strap strength.