A method and apparatus are provided for forming two-piece drinking cups and containers from conventionally shaped arcuate sidewall blank and bottom blanks of filled polypropylene sheet material or polypropylene-polyethylene copolymer sheet material with approximately 40% talc or calcium carbonate as a filler. The arcuate blanks for the sidewall and the bottom blanks are run through relatively standard two-piece container or cup making machinery utilizing patterned air jet heating means to heat areas of the filled plastic sheet material such that the sidewall and bottom curl seams can be heat sealed on the forming mandrels of the machinery and the top curl can be placed in the container by heating and substantially conventional forming dies. The seaming structures so produced are extremely water tight and of high strength characteristics.