In the design of a polymer extrusion system the residence time distribution (RTD) is a common characteristic to evaluate the process, for example regarding mixing efficiency, changeover time, process monitoring or traceability of product quality. The experimental determination of the RTD is usually performed by injecting a defined concentration of a tracer substance at the system inlet and measuring its response in terms of outlet concentration over time. While many studies investigating the system behavior of single- and twin-screw extruders already exist, to date, only few scientific publications deal with the measurement and analysis of the RTD of an entire blown film line. In this context, this paper presents the results of RTD experiments on a small-scale blown film line, using a masterbatch as tracer substance and colorimetry for concentration measurement. A comparison of the pulse input and step input injection method at varying concentration levels is drawn. Measured data are evaluated with a routine and fitted in two different ways, using a Weibull and the lognormal distribution. The study confirms that tracer experiments with colorimetry are appropriate for a qualitative analysis of a blown film extrusion line. However, a quantitative analysis might have limited significance in practice, unless the experimental conditions, such as the tracer input method, and the evaluation routine are specified accurately.