Hydrocarbons (C-8 to C-12) with specific chemical nature and constitution are used to investigate their plasticizer efficiency with regard to low-temperature flexibility and processing behavior. Irrespective of the nature of the rubber used the highest plasticizer efficiency is observed in the order of the molecule structure: linear branched > cyclic. The efficiency region of the hydrocarbons is limited by the critical solubility concentration which is increases inversely from cyclic to linear hydrocarbon structures. It is demonstrated that the plasticizer efficiency is increasing when the radius of gyration of the molecule increases. Similarly graded influences from the free volume or the thermal expansion coefficient of the hydrocarbons are established.