In industrial practice involving mixtures of raw materials, it is desirable to be able to predict how a change in their proportions will affect the product's properties. In this work the effect of three major vulcanized rubber raw materials was investigated. All other raw materials, as well as processing conditions, were kept constant. Ten formulations were vulcanized by compression moulding (175 8C, $17 MPa, during 5 minutes) and characterized. The statistically valid property equations calculated from the characterization results show that a range of compositions exists within which the final product has the desired properties and can still be comfortably manufactured.