The presence of a three-dimensional network of high-aspect-ratio CO2-philic fibers increases the extensional viscosity of melts but decreases the shear viscosity under a CO2 atmosphere. The generation of such a rheological response is rare in literature because the addition of solid-state fibers typically increases both extensional and shear viscosities. These results are supported by the high-pressure rheological characterization of polypropylene (PP) containing various loadings of polytetrafluoroethylene (PTFE) fibers. While the shear viscosity decreases with an increase in fiber loading due to the higher uptake of CO2 from the CO2 philicity of PTFE, a strikingly different behavior is seen in extensional flows: below the fiber percolation threshold, the extensional viscosity decreases; however, above the percolation threshold, the extensional viscosity jumps by an order of magnitude. The enhancement in extensional viscosity is attributed to the large resistance offered by the network against extensional deformations. These results have important consequences in CO2-based polymer processes.