The aim of this Letter is to re-investigate the characterization of ice porosity. N-2, CH4 and Ar adsorption on amorphous ice has been compared to that on crystalline ice at low temperatures, using adsorption isotherm volumetry and infrared spectroscopy simultaneously. Here we show that amorphous ice can present a large specific surface area and nevertheless be non-microporous; this provides new ways for the understanding of interstellar reactivity. (C) 2002 Elsevier Science B.V. All rights reserved.