Abstract: A method of blow-molding comprising forming a parison (tube) of a thermoplastics material, closing a mold around the parison, injecting compressed gas into the parison through a blowing hole to form a molded product that is shaped according to the shape of the mold, then deforming a seal forming portion of the molded product with a heated sealing tool to seal the blowing hole. The seal-forming portion may comprise a tubular collar that surrounds the blowing hole.