Exploring the limits of broadband 90° and 180° universal rotation pulses

► A systematic study of performances of universal 90° and 180° pulses is presented. ► Pulses were studied with respect to bandwidth, pulse length, tolerance to B1-inhomogeneity. ► The majority of time-optimal pulses belongs to one of two specific symmetry classes. ► BURBOP pulses found are shown to perform better than previously published pulses. ► UR 180° pulses perform better than two consecutive PP inversion pulses in INEPT steps.