A downhole system includes a packer sealing an annular space around a downhole tubing and an insulating packer fluid positioned within the annular space and adjacent to the packer. The insulating packer fluid includes a sodium bicarbonate activator and an acidic nanosilica dispersion having silica nanoparticles and a stabilizer, wherein the pH of the acidic nanosilica dispersion ranges from 2 to 5, and the silica nanoparticles form at least 20 percent by weight of the acidic nanosilica dispersion.