<p>Elastomeric blends are used for various applications by balancing factors like processibility, performance, and cost. The tailored properties like electrical conductivity, dielectric permittivity, electromagnetic interference shielding, etc. make these blends ideal for specific high-tech applications, while basic properties like tensile strength, thermal stability, and aging resistance remain key to their general effectiveness. Chloroprene rubber (CR) and Bromo butyl rubber (BIIR) blends reinforced with extremely porous electrically conductive Ketjenblack (KB) by varying loadings (0,5, 10, 15, and 20 parts per hundred rubber) were prepared. The key focus of the study is to analyse the effect of KB (BET surface area 1347 m²/g) on the cure characteristics, mechanical thermal, and dielectric properties of the composites. The tensile strength of the composites improved by 31.0% corresponding to 10phr of KB. Thermal aging studies reveal that tensile strength retention of all the composites is more than 90%. XRD analysis shows that adding KB resulted in a more ordered arrangement of rubber chains, improving the crystalline structure. The thermal stability at 50% degradation is increased by 10ºC and 17ºC for 10phr KB and 20phr of KB composites respectively. The AC conductivity reveals a percolation threshold, corresponding to 15phr of KB loading. Dielectric constant and dielectric loss were significantly improved as the KB loading crossed the percolation threshold. EMI shielding effectiveness of 33dB was obtained for 20phr of KB, which attenuates more than 99.94% of electromagnetic waves. These advanced composites are an exceptional promise for critical aerospace and defence applications where electromagnetic protection is highly significant.</p> Graphical abstract <p></p>