Structurally tailored and engineered macromolecular (STEM) gels are polymer networks containing latent initiator sites available for postsynthesis modifications. The STEM gels presented here were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, and the network was modified by grafting soft poly(n-butyl acrylate) (PBA) side chains via atom transfer radical polymerization (ATRP) to create supersoft materials. Modified STEM gels with low Young’s moduli (E = 590–220 kPa) were produced, and the mechanical properties were tunable by varying the grafting density and side chain length. Dissipative particle dynamics (DPD) simulations were used to gain insight into side chain mobility in the network. This approach was also used to made soft elastomers (E = 42 kPa), which could withstand 100% shear strain without permanent deformation. Using spatial control, single-piece materials with hard or soft domains were synthesized.