One of the components of aluminum, crimp fiber optic splice protectors is a modified polyisobutylene mass (PIB). It protects the fiber optic splice against climatic factors, pollution and mechanical damage. It stabilizes the optical fiber in a specific location, not allowing it to move. It must maintain its unchanged properties for several dozen years. Industry standards define what property PIB mass should have. These properties are determined by the use of a viscometer. Our laboratory is able to test the viscosity of liquid materials. We use a rotational viscometer for this purpose. The measure of viscosity is the value of the force acting between two coaxial cylinders: a fixed outer cylinder and an inner cylinder rotating in relation to it, the tested mass fills the gap between the cylinders. The above force is expressed in dynamic viscosity, the unit of which is Pauz [Pas]. To determine the viscosity, we use the THERMO HAAKE RotoVisco 1 device from the American company Thermo Fisher Scientific Inc .. The above device allows us to measure in the range from 1 to 100,000,000 mPas. The measurement results are visualized using the HAAKE RheoWin Software.