Abstract: Apparatus and method are provided for heat-sealing multi-ply layers of thermoplastic film comprising a rotating drum having at least one outwardly opening recessed area extending across the surface thereof essentially parallel to the axis about which the drum is rotating; heat sealing means movably mounted within the recessed area of said drum; means for supporting a continuous ribbon of multi-ply layer of heat-sealable thermoplastic film about at least a portion of the peripheral surface of said drum and bridging the recessed area therein; means for traversing said heat sealing means in a radial direction within the recessed area of said drum between a retracted position with the heat sealing means totally within the recessed area of said drum and an extended position with the heat sealing means projecting beyond the surface of said drum; and means for discharging seamwelded film segments from about said drum.