Spin-on glasses are candidates in the microelectronics industry as low dielectric constant insulating layers. Spin-on glasses are very brittle materials. This paper discusses measurement problems as relevant to the characterization of a brittle material by the indentation technique. As for all polymeric materials curing temperature is the most important preparation parameter. There is a correlation between hardness, Young's modulus, the onset of cracking with curing temperature. This dependence on curing temperature is also expressed by the change in Si-H bond density as shown by FTIR data. Life expectancy or aging characteristics were also investigated for these features. As an example results on silsesquioxane spin -on glasses are presented.