Abstract: A retroreflective marking material is disclosed comprising a sheet having at least some light-transmitting portions, a light-refracting surface on one side, and a plurality of trihedral light-reflecting units of three mutually perpendicular facets on the other side adapted to be adhered to a working site. The light-reflecting units are oriented to reflect light having relatively high angles of incidence with respect to the sheet. The marking material may be used as a tape for marking roads and is effective whether wet or dry. Optionally, the sheet or tape has light-receptors which rise above the tape and are spaced apart along one direction of the tape, and the trihedral light-reflecting units are substantially opposite the light-receptors. Preferably, the light-reflecting units have the shape of a triangular-based pyramid, and the marking material retroreflects the light in two opposite directions.