Polymer modification is a way to obtain binders with improved mechanical properties. Adding polymer to bitumen allows to greatly improve its high temperature rheological properties, leaving the low temperature ones only slightly better.

More specifically, a rule of thumb states that for every 1% of added polymer, 2ºC in high temperature Performance Grade (PG – see RoadMat Note 2) are typically gained. On the low temperature end, the rule becomes more 1% of added polymer, gives 1ºC in low temperature PG for SB type modifiers mostly. Since the PG classes are based on 6ºC steps, the typical modification with 3% elastomer or plastomer (see below), generally allows gaining one high temperature class leaving the low temperature generally unchanged. A 6% modification, especially with elastomer, could allow gaining 2 high temperature classes (12ºC) and one low temperature class (6ºC).

Another rule of thumb states that an operating range (limiting high temperature minus limiting low temperature) higher than 95ºC can only be obtained through bitumen modification.