Aspects of the disclosure relate to techniques for manufacturing a balloon envelope. In one example, a first sheet of material for a first gore of the balloon envelope is provided. Lap seal material is arranged at least partially on the first sheet of material. A first heat seal is created between the lap seal material and the first sheet of material. A second sheet of material for a second gore of the balloon envelope is arranged over the first heat seal. A second heat seal is created between the lap seal material and the second sheet of material such that the lap seal material is configured to provide additional structural support to the balloon envelope.