To select the optimal concentration of resin in initial sol which was embedded in polyester mat insulator, criteria
of lightness, flexibility, thermal conductivity, and thermal diffusivity are very important. With novolac aerogel mass
fraction in insulator increase, insulator will become heavier and its flexibility will decrease. So the samples with
concentration of resin in initial sol less than 20 wt. % are appropriate. Thermal conductivity plays an important role
in choosing the adequate thermal insulator which is appropriate for PEm 15. Based on this research, because of having
good thermal properties, the PEm 15 sample has an optimal resin concentration in initial sol.