Provided herein is a liquid-filled, non-reclosable tetrahedral or pillow-shaped packaging container having a longitudinal fin seal and a pair of transverse seals. In the case of tetrahedral packages, the transverse seals are perpendicular to one another. Also provided herein is an apparatus for the formation of such fin seals as part of a continuous packaging and filling operation. A third aspect of the apparatus of the present disclosure is the development of a heated jaw that exhibits consistent heating across the jaw face. Yet another feature of the apparatus of the present disclosure is provided in a modified, closed-loop electrical system for real-time monitoring and adjustment of the temperatures of the heated jaws, as they are moving.