Top: supernova remnant properties across the forward shock surface at 2 kyr, extracted from the hydrodynamical simulation shown in Fig. 3. Bottom: integrated maximum energy at 2 kyr for the resonant and non-resonant streaming instabilities (RSI and NRSI, respectively) and without streaming instabilities. B_eq was computed assuming that 10% of the kinetic energy in the superbubble goes into a turbulent magnetic field.