Container fabrication method

A method of fabricating a fluid-tight container from an integral sheet of thermoplastic film coated paperboard comprising the steps of:

• folding a tubular enclosure having four side walls laterally delineated by substantially parallel corners;
• forming a fluid-fight bottom wall that is substantially perpendicular to said tubular enclosure corners with bottom peels that are materially integral extensions of said side walls, by lap folding said bottom panels;
• sealing said bottom panels fluid-tight by heat fusing the thermoplastic coating respective to continuous surfaces of said bottom panels;
• and
• embossing said bottom wall to a substantially concave surface shape with a set of embossing dies so that said bottom wall has at least three substantially parallel planar areas of concentrically diminishing areal magnitude aligned in a stepped sequence, while allowing the gas created by the embossing step to be vented through an air channel in at least one of said dies.