Synthetic casings have recently been found to prevent the penetration of carcinogenic compounds in meat products during smoking, in contrast to natural casings. In this paper, physical characteristics of 48 chorizos encased in natural (ChN) and synthetic (ChS) casings, during 11 days of direct smoking, were compared by means of texturometry, colourimetry, moisture, Scanning Electron Microscopy and Fluorescence Stereo Microscopy analyses. The lightness (L*) of ChS is lower (p = 0) than ChN. During 5 days, ChS presented higher hardness and browning index, and less redness (a*), yellowness (b*) and chroma than ChN (p < 0.05). At 7 days, no differences (p > 0.05) were found in a*, b*, hue angle or chroma. Except at 1 day, no differences (p > 0.05) were found in their moisture. Physical characteristics were suitable in both cases, but synthetic casing reduces production time, prevents the penetration and accumulation of soot particles in mass cavities, and enables the standardization of chorizo.