A high voltage electrical insulator formed from a curable liquid silicone rubber composition, and subsequently cured, a composition consisting essentially of(A) 100 weight parts of a fluid mixture of polyorganosiloxane comprising(a) at least 5 weight percent of a polyorganosiloxane resin comprising repeating units selected from the group consisting of SiO.sub.4/2 and RSiO.sub.3/2, where R is a monovalent hydrocarbon group, and(b) polydiorganosiloxane having a viscosity in the range from about 100 mPa.multidot.s to 100,000 mPa.multidot.s, that contains at least 2 silicon-bonded alkenyl groups in each molecule,(B) 1 to 100 weight parts microparticulate silica,(C) polyorganohydrogensiloxane that contains at least 2 silicon-bonded hydrogen atoms in each molecule, in a quantity that provides a value from 0.5:1 to 20:1 for the ratio of the number of moles of silicon-bonded hydrogen in the instant composition to the number of moles of silicon-bonded alkenyl in component (A), and(D) a catalytic quantity of a platinum catalyst.The liquid silicone rubber composition, prior to its cure, evidences a desirable fluidity and excellent moldability. Upon its cure the composition produces very mechanically strong silicone rubber moldings that have excellent high-voltage insulating properties tracking resistance, erosion resistance, arcing resistance without the use of fillers such as aluminum oxide, aluminum hydroxide or quartz.