Flux‐trapping during the early formation phases of a field‐reversed configuration has been studied experimentally on the field‐reversed theta‐pinch TRX‐1. An annularz‐pinch preionizer was employed to permit ionization at high values of reverse‐bias flux. Contrary to previous analysis, the rate of flux loss was not governed exclusively by inertially limited plasma convection to the tube walls. At high reverse flux levels, a pressure bearing sheath was observed to form at the tube walls and the flux loss was restricted by resistive diffusion across this sheath. The characteristic time for flux loss was 0.08rt(cm) &mgr;sec, independent of the bias field and independent of the fill pressure for fill pressures above 15 mTorr D2. Octopole barrier fields were found to be effective in limiting the inertially governed flux loss at very early times before the wall sheath formed.