Injection molding companies are now regularly using a procedure called Gas Assisted Molding utilizing nitrogen gas to produce unfilled hollowed out gaps within the plastic-part the injection mold creates. At the finish of the filling stage, the gas (N2) is being injected to the still liquid core of the molding. At this time the nitrogen gas requires the most convenient road to minimum resistance (very similar to water does); after which takes the place of the heavy liquefied things with gas-fulled segments. At this point there is pressure applies by the gas which compresses the plastic resin strongly to the injection mold outside, all the while adjusting for the amount of volume and downsizing; continuous till the plastic part becomes solid. Eventually, the gas is vented to atmosphere or re-cycled.