Poly(urethane acrylate) aerogels were synthesized from radical polymerization of a dendritic monomer having an isocyanurate-based rigid/aliphatic core, urethane linkages and nine terminal acrylate groups. The rigidity of the core comes from the triisocyanate, an isophorone diisocyanate trimer (IPDI). The material properties of those aerogels were compared to the properties of related literature materials derived from triisocyanates with flexible/aliphatic or rigid/aromatic cores, bearing (a) three, or (b) nine terminal acrylate groups. Data support that material properties such as the primary particle size and the BET surface areas are determined mainly by the degree of crosslinking (i.e., the monomer multifunctionality), while the molecular rigidity vs flexibility of the triisocyanate core plays only a secondary role. Addition of ethylene glycol dimethacrylate (EG) in the sol as a chain extender increased the hydrophilicity of the aerogels and their ability to absorb water.