Viscosity

The viscosity of the polymer is a measure of the material’s resistance to flow. A material which flows easily has a low viscosity, while a material with a higher viscosity does not flow as easily.
Most polymers are available in different grades, each grade has its own flow characteristics. Typically, materials with lower viscosity’s have lower molecular weight. These materials are easier to process, but typically have lower mechanical strength than the same polymer with a higher viscosity.
The viscosity of the polymer can be used to compare the flow characteristics of different polymers, or different grades of the same polymer.
Viscosity data can also be used to qualify a new material. You can compare a newer lot of material to a previously used material to determine whether or not the new material is the same.
Two of the most common methods of determining viscosity are capillary rheometry and melt flow indexing.