Abstract: The instant invention broadly relates to a process and apparatus for filling a cavity with a reactive mixture. More particularly, the invention relates to a process for filling cavities, particularly mold cavities, with a reactive, flowable mixture which preferably forms foam, wherein at least two reaction components are brought into a mixing zone, where they are mixed and then brought into the cavity, the improvement wherein at the beginning of the filling process, during a limited time interval, the reaction mixture is fed into the cavity under low flow velocity until the mixture has reached a certain level in the cavity, and subsequently the remaining mixture to be injected, is fed in under increased flow velocity.