In contrast to heavy CO₂-intensive traditional functional fillers used by the rubber and plastics industry, UPM’s RFF features a much lower material density. Determination by volumetric gas pycnometry according to ISO 21687 yields values of only 1.3 g/cm³, which, compared to carbon black and precipitated silica, is more than 25% and 35% lower, respectively. Inactive, inorganic white fillers like kaolin, talcum, or siliceous earth are even twice as heavy. This unique natural feature of RFF allows for significantly reducing the overall compound [or article] weight. Depending on the compound design (i.e. rubber type, filler to be replaced, and actual filler loading), final weight savings up to 25% can be achieved. Lightweight materials have always been an essential topic in product design across several industries. Nowadays, the concept has been essential in the automotive industry regarding better fuel economy. Here, the critical driver for lightweight materials is to compensate for the heavyweight of the batteries in electric and plug-in hybrid vehicles.