Numerous PLA resins have already been tried with chemical blowing agent and physical blowing agent on extrusion process to study the expansion dependency of amount of blowing agent and cell density, respectively. It has been found that a `dip' is present in both instances; foam density decreases to a minimum, then increases. It implies competing mechanisms during foaming. Bubble development model with area vaporization shows up inadequate in describing the counterintuitive foam density rise at improved blowing agent loading. Investigating foam rod diameter implies premature gas separation from the polymeric melt before foaming happened at a higher gas loading. It influences foaming efficiency adversely. Also discussed mixer extruder is the foam density variation during aging.