The reaction of suitable organic compounds such as omega-halo-1-alkenes, allyltrichlorosilane or 2-methyl-3-butyn-2-ol in combination with a well-defined inorganic silsesquioxane, H8Si8O12 A cores, leads to covalently bound organic-inorganic hybrid materials in high yields. The hydraulic fluid properties of these viscous hybrid materials were evaluated and compared with those of some commercially available hydraulic fluids: Mobil EAL 224H, Super-V (AP) and Puroil SHO. The results showed that most silsesquioxane semi-liquids possess hydraulic fluid properties comparable to those of the 3 commercial lubricants.