The default artwork you purchase here under the collection pages are all made on the HD metal aluminium that has a 2mm thick profile. The surface is glossy, colors are well saturated and with such a high contrast and sharpness that earns its name of High Definition Aluminium. * NOTE: The GS/GM gift size HD metal art do NOT include a hanging rail element (which can be added upon purchase for $14USD). It is for the purpose that you can easily customise your frame with those 2 common sizes.