Glycoprotein B (gB) refolds between prefusion and postfusion conformations to facilitate herpesvirus entry into host cells. However, the isolation of prefusion-specific neutralizing antibodies, effective against other viral entry machines, has been challenging. Here we describe stabilization of the prefusion gB ectodomain from herpes simplex virus 1 (HSV-1), determine ectodomain structures at 2.9- to 4.1-Å resolution using cryogenic electron microscopy (cryo-EM) and isolate a prefusion-specific gB-neutralizing antibody termed WS.HSV-1.24. Murine immunization with gB stabilized in the prefusion conformation induced high titres of antibodies binding to both prefusion and postfusion gB, but-most notably-without measurable serum neutralization. Accessibility analysis revealed iso-surface exposure, with accessible surfaces on prefusion HSV-1 gB also exposed on postfusion gB. Structural analysis suggested substantial plasticity, with regions that refolded between pre- and postfusion conformations relegated to domain interfaces with limited accessibility; indeed, WS.HSV-1.24 recognized a domain-interface refolding region to facilitate neutralization. We propose that prefusion HSV-1 gB evades neutralization by most antibodies through an iso-surface display that is coupled to structural plasticity.