The present invention relates to polymer blends comprising: (a) from 5 wt % to 95 wt % of a HDPE having a density from 0.941 g/cm3 to 0.980 g/cm3 and an I22 of 10 dg/min or more; and (b) from 95 wt % to 5 wt % of a grafted mPE, which is a reaction product of (i) a mPE having a density from 0.860 g/cm3 to 0.935 g/cm3 and an I2 from 0.7 dg/min to 5.0 dg/min, and (ii) a silicon-containing grafting component, wherein the blend exhibits a high-temperature creep after extrusion that is at least 20% lower than a blend of the HDPE and the mPE that has not been grafted with a silicon-containing grafting component. These blends can advantageously comprise at least one layer of a film, e.g., made via extrusion.