Certain classes of sol-gel transition have been modeled as diffusion-limited cluster-cluster aggregation (DLCA), but it produces excessive dangling branches on the resulting network that underestimates the rigidity of gels. The “dangling bond deflection” (DEF) model was developed to simulate spatial fluctuation of the dangling branches under thermal energy. Collision and sticking of two dangling branches within the same cluster turns these branches into a loop. Combination of the DLCA and DEF models creates network that possesses extensive loop structure and negligible dangling mass. The networks are substantially stiffened by the loop structure, and successfully reproduce the empirical scaling relationship between linear elastic modulus and density exhibited by real aerogels. The gel structure can be represented by the “blob-and-link” model, in which blobs refer to dense, rigid collections of particles, interconnected by tenuous links of particle chains. When the network is deformed, only these few weak links contribute to the stiffness, leaving the blobs unstrained. The gel modulus drops significantly as porosity increases because more particles reside in the blobs and fewer particles carry the strain.