Reducing the melt index of TPU (Thermoplastic Polyurethane) can indeed affect the hardness of the material, but it's not a direct correlation. The melt index refers to the flowability of the molten TPU during the injection molding process.

Generally, a lower melt index indicates a higher molecular weight of the TPU, which can result in increased hardness. This is because higher molecular weight TPU tends to have a more tightly packed structure, leading to a stiffer material with higher hardness.

However, other factors such as the specific formulation of the TPU, the presence of additives or fillers, and the processing conditions can also influence the hardness. So, while reducing the melt index may contribute to increased hardness, it is not the sole determining factor.