Inner liners are used in every tyre to prevent the air from escaping. As the inner liner is a characteristic relevant to safety of every tyre, there are high requirements for compliance with the target data. An important criterion is the layer thickness. The system for measuring the thickness of inner liners operates without contact and wear-free. The inner liner is routed through the measuring system immediately after the calender roller. A measuring head traverses above the surface. An eddy current sensor measures the distance to the reference roller while an optical micrometer measures the distance to the rubber surface. The system can be integrated in the heating circuit of the calender roller for better temperature compensation.