To quantify the internal free surface in various resin cements and glass-ionomer-based materials.Materials tested were Nexus fluid (NXF) and viscous (NXV), Vitremer (VTM), Fuji II LC (FII), Vitremer Luting Cement (VLC), Dyract (DYR) and Compoglass (COM). Samples (n=5) were made of each material between two microscopic glass slides under same weight. With a transmitted light microscopy, four zones of each sample were evaluated, finding the number of porosities per mm2 (NP), the average radius of porosities (RP), the ratio of total area of surface porosities (micron2) to area (mm2) of specimen surface (TA) and the ratio of total volume of porosities (micron2) to area (mm2) of material surface (VP).Median test was used. NP: NXV, NXF and DYR had smaller NP than VTM and FII and (likely) than VLC (P> 0.0000001). RP was smaller for DYR than for VLC and (likely) than for NXV (P= 0.00019). TA: NXV, NXF and DYR had smaller TA than VTM, FII and VLC (P< 0.0000001). VP: NXV and DYR had smaller VP than FII and (likely) than VTM and VLC (P< 0.0000001).