The study of multiphase flow within microscale geometries has garnered much attention in recent history. One system of interest is the flow of a low viscosity fluid thread, labeled as the coring fluid, through a much higher viscosity liquid, labeled the coating fluid. On the macro-scale, this process has shown great utility in the plastics industry, but it has yet to be completely characterized on the micro-scale. Detailed here is a set of experiments performed within square microchannels, of nominal area 250 lm by 250 lm, where the coring fluid was Newtonian and the coating fluid was either Newtonian or viscoelastic. Visual data were collected and subsequently analyzed to determine the thickness of coating fluid remaining on the walls of the microchannel after the coring fluid front passed. The results for flow through a Newtonian coating fluid show similarity to results for flow in macro-scale capillaries; the thickness of the coating fluid, after initial penetration by the coring fluid thread, follows the same dependence upon the velocity of the thread front as seen for the macro-scale. The case of a viscoelastic coating fluid in a microchannel, however, shows interesting differences to the macro-scale results. Most notably, the surface of the coring fluid thread was highly unstable and the entire thread migrated toward one wall.