High quality sports goggles are mandatory wear in a variety of activities. Often visual or mechanical properties are important for safety, but also for proper enjoyment of the sport. In the Paralympic sport of goalball, for example, the goggles must completely block out the user from all visual perception. Additionally, some goggles are designed with thermal properties in mind to help prevent the inside lens from getting too cold and ‘misting over’. 

The imperfections resulting from poorly implemented injection molding compromise the goggles and their effective use. Melt fractures induce stress concentrations which inhibit durability; rapid solidification results in insufficient mold filling which causes discomfort and inhibits insulation. Also thermal degradation can affect the physical properties of the goggles, making them weaker. The capillary rheometer simulates the injection molding processes by imposing a defined shear rate on the thermoplastic melt. The pressure experienced by the melt is measured, and flow stability or instability can be determined.