Aspects of the disclosure relate to manufacturing a balloon envelope for use in a stratospheric balloon system. For instance, a stream of polyethylene mixture is extruded through an extruder in order to orient molecules of polymer chains of polyethylene and to provide an oriented film. The oriented film is passed through an electron beam and thereby crosslinking the polymer chains to provide a cross-linked film. The cross-linked film is heat sealed to form the balloon envelope.

A method of manufacturing a clamping ring for a cold-expansion joining system includes providing an extruded pipe part made of a cross-linked polymeric material where, while extruding the pipe part, the inner diameter is formed bigger than the outer diameter of a flexible cross-linked polymeric pipe onto which the clamping ring is positioned before making a pipe connection; providing an injection molded annular part having an inner diameter formed smaller than the inner diameter of the extruded part; and bonding the parts together to form a clamping ring having an inward protruding stop edge at one of its ends. The embodiments further relate to a clamping ring formed from an extruded pipe part made of a cross-linked polymeric material and an injection molded annular part bonded together to form a unitary structure including an inward protruding stop edge at one of its ends.

Stereolithography with micron scale control of properties is described herein. In one aspect, a computer-implemented method for 3-D printing of a material can include generating a functional relation predicting one or more physical properties of the material resulting from printing parameters; algebraically or numerically solving the functional relation to generate a second functional relation predicting expected printing parameters resulting in the one or more physical properties; and printing the material via a photopolymerization printer according to the set of printing parameters determined by the second functional relation.