A method of fabricating plastic products having a preselected characteristic, comprising preparing a dispersion of at least one additive contributes the preselected characteristic in cottonseed oil; supplying a preselected plastic resin for the product to be fabricated to a process machine having a rotating screw; furnishing the dispersion to the process machine at a position adjacent to threaded portion of the rotating screw; and blending the dispersion and the resin by rotating the screw.

A liquid colorant for use in molding or extruding plastic products comprises pigment dispersed in cottonseed oil.

Single, continuous PTFE layers having lateral zones of varied characteristics are described. Some of the lateral zone embodiments may include PTFE material having little or no nodal and fibril microstructure. Methods of manufacturing PTFE layers allow for controllable permeability and porosity of the layers, in addition to other characteristics. The characteristics may vary from one lateral zone of a PTFE layer to a second lateral zone of a PTFE layer. In some embodiments, the PTFE layers may act as a barrier layer in an endovascular graft or other medical device.