Optical defects such as fish eyes or holes can have a detrimental effect on the web quality and can even lead to its rejection. Therefore, web inspection systems which have been used in the steel and I,a),Rr industries for quite some time, have become an important instrument of duality assurance in the plastics industry. The systems which are currently available in the market are equipped for the detection of fish eyes, holes but also contaminants, tears, coating errors, scratches, gel particles, streaks, bulges or thin areas.