The Melt Flow Index (MFI) is a measure of the ease of flow of the melt of a thermoplastic polymer. It is measured by placing the polymer in a heated chamber, the melted polymer flows through a capillary rheometer: the weight of the polymer leaked in a given time corresponds to the Melt Flow Index. The greater the weight of the leaked material, the higher the Melt Flow Index, the lower the viscosity of the polymer.