To better understanding the flow and heat transfer mechanisms of refrigerants flow boiling in metal-foam filled tubes, the two-phase flow patterns of R410A were observed in two 7.9 mm inner diameter horizontal tubes filled with 5 or 10 PPI (pores per inch) copper foams. The mass fluxes were 90-270 kg m(-2) s(-1). The results show that slug flow, plug flow and annular flow occur in sequence with the increase of vapor quality. The transitions from slug to plug flow happen at lower vapor qualities with the increase of mass flux or metal foam PPI, while the transitions from plug to annular flow happen at vapor qualities around 0.4. The metal foam promotes the formation of annular flow and the effect is stronger with the higher PPI metal foam. A flow pattern map was developed that combines data from the present study and previous studies for flow patterns in metal-foam filled tubes. (C) 2015 Elsevier Ltd. All rights reserved.