In the plastics industry, measuring the melt flow rate (MFR) is one of the simplest and most frequently used test methods for finding out about the flow behaviour of polymers. The following case, taken from actual practice, will show that this method of determining the melt characteristics of a substance is not always sufficient. The two LDPE (low-density polyethylene) samples in this investigation both had the same MFR value, but displayed different modes of behaviour in practice when they were being processed.