A method and apparatus for sealing a bag made of a polymeric material by applying heat activated layers on different portions of the bag, wherein the first adhesive layer and the second adhesive layer have respective heat activation temperatures below the softening point temperature of the polymeric material; after creasing the bag along a fold line, applying heat at a temperature below the softening point temperature of the polymeric material to activate the first adhesive layer and the second adhesive layer to adhesive states after the bag has been filled with contents; and folding the bag to form an adhesive-to adhesive seal by contact between the heat activated first adhesive layer and the heat activated second adhesive layer.