Although glass-RuO2 composites are well known for their particular electrical properties, the reasons for their very low percolation thresholds are still subject to debate. In this paper, a detailed study of the influence of various experimental parameters (temperature, RuO2 content, stirring, etc.) on the electrical conductivity and, in particular, on the percolation threshold in borosilicate glass-RuO2 composites is presented. This percolation threshold is shown to increase by a factor of two (from 0.6 to 1.2 vol%) when stirring is applied during synthesis and by more than a factor of three (> 2.1 vol%) when a sol-gel route is used. Besides, the study of various synthesis temperatures reveals that the electronic part of the electrical conductivity is highly correlated to Ru solubility in the glass matrix. It can be concluded from these various experiments that both the presence of dissolved ruthenium in the glass matrix and the possibility of RuO2 particles to rearrange in the melt in order to form kind of a network are necessary for a low percolation threshold.