This paper demonstrates an adhesive mechanism for wall slip by showing experimental results obtained using low surface energy fluoropolymer-coated die walls. A transparent slit die is constructed to allow direct flow visualization of wall slip. By ＇coloring＇ polybutadiene and polyethylene with carbon black and coating the lower half of the slit die wall with a fluoropolymer, we show by visual inspection that the blackened polymers stick to the clean half of the die wall and slip over the coated portion. (C) 2000 Elsevier Science B.V. All rights reserved.