This article is intended to examine how precipitated silica could be used in a cobalt boron complex-promoted adhesion system without the use of a resin. The objective is to decrease hysteresis (rolling resistance) together with an improvement of some adhesion properties. In a compound containing a cobalt boron complex, the partial substitution of carbon black by precipitated silica leads to an improvement in retained adhesion after salt water ageing. By choosing low specific surface area silicas, such as Zeosil 85 or Zeosil 125, in conjunction with TESPT (Si69), it is possible to obtain a steel belt insulation stock with a low hysteresis, improved tear resistance and improved retention of adhesion after heat, humidity and salt water ageing.