To optimise the side streams in the compounding process, FEDDEM has developed a modified FSB side feeder, which sucks air out of the metered side stream before it enters the extruder. When adding materials with lighter bulk density, this enables a considerable increase in the throughput rate of the entire process. Compared to conventional side-feeding of low-bulk-density additives, the throughput of the compounding line could be increased several times over. In some applications, economically viable production rates only became feasible with the use of an FSB-V side feeder.