A cone calorimeter can provide material "reaction to fire" information for use in evaluating the fire hazard of materials. Two orientations can be selected, vertical or horizontal, depending on the geometry of materials in their final use. However, most fire models and material evaluation reports fail to consider the effects of the orientation and applied the horizontal case data. To assess the validity of using data with "horizontal" samples for further applications, a systematic experimental was performed using materials including PMMA, wooden products and polystyrene foams. Besides critical heat flux for ignition, other "reaction to fire" material properties were measured, including ignition time, ignition temperature. heat release rate history and mass loss rate when exposed to three heating irradiances, namely 15, 30 and 50 kW/m(2). For the horizontal orientation in comparison to the vertical orientation, the study data reveal relatively constant temperature distribution before ignition, lower critical heat flux for pilot ignition, shorter time to ignition, lower peak heat release rate, identical total heat release, longer burning time and almost identical combustion completeness for all the tested materials except polystyrene foams. Ignition temperature displaced no clear trend. Vertical orientation tests are consequently recommended for evaluating material fire performance. (C) 2009 Elsevier B.V. All rights reserved.