A Cap arrangement comprises an opening-indicator device that has an outer edge wherefrom leads away fin members which in use extends towards the inside of said cap arrangement, said fin members comprising, in one of their portions nearest said edge, an elongated element having a substantially rectilinear extension, said fin members further comprising, in one of their portions further away from said edge, a flexible appendage elements; a cap arrangement comprises an opening-indicator device that has an outer edge wherefrom leads away fin members comprising a first portion suitable for interacting with a surface of a first collar arrangement extending radially from a neck of container arrangement, a second portion suitable for interacting with a further surface of a second collar arrangement extending radially from said neck and a third portion suitable for interacting with a yet further surface of said first collar arrangement.