Nature Materials, Published online: 03 June 2026; doi:10.1038/s41563-026-02604-8Polyelectrolyte elastomers support selective and leakage-free ionic transport, but suffer from low ionic conductivity. A solid-state dielectric additive is introduced to various polyelectrolyte elastomers, which increases ionic conductivity by two orders of magnitude and maintains elasticity and leakage-free properties.