Knowledge
MFR and Cycle Time in Small Bottle Molding
2026-09-20 · Ascent Group Editorial
Melt flow rate is the closest single number to line output in small-article blow molding. Higher MFR means the melt moves with less pressure, fills detail faster and freezes sooner because less shear heat is stored in the part.
But MFR is not free: very high flow grades trade away some stiffness and stress crack resistance. The art is matching the grade to the article: a household bottle needs both speed and strength, a toy hollow body mostly speed.
B5635G at MFR 35 serves the first case; buyers who need maximum stiffness at the same size move one step down the flow ladder to B5823 and accept longer cycles.
