DNP enhanced NMR with flip-back recovery.

•Combining MAS DNP with flip-back yields up to a factor 3 increase in overall sensitivity.•Flip-back provides up to a 10-fold reduction in recycle delays.•The method can be applied to bulk solution or to impregnated samples.•Relayed polarization models reproduce the experimental behaviour.•Overhauser effect DNP enhancements of over 70 are reported at 592 GHz/900 MHz.