The question of slip and the influence of materials of construction on the observed extrudate irregularities are examined for high viscosity molten polyethylenes. Capillary rheometer studies were conducted for several linear (LLDPE and HDPE) and branched (HP‐LDPE) polyethylenes, Viton A, and Barex‐210. Extensive blown film fabrication studies were conducted for narrow MWD UNIPOL process LLDPE resins. The results indicate that the assumption of “no‐slip at the rigid boundary” is generally not valid for polyethylenes above a critical shear stress of approximately 0.1–0.14 MPa, when either surface or gross irregularities are present in the extrudate. Loss of extrudate gloss at the critical shear stress defines the onset of melt fracture. Within the range of variables examined, the critical stress is relatively insensitive to molecular characteristics (molecular weight, MWD, and chain branching), melt temperature, and the detailed design of the capillary. Contrary to capillary rheometer observations, blown film fabrication results for LLDPE indicate that materials of construction for the die land region have a significant influence on melt fracture, and suggest breakdown of adhesion at the polymer/metal interface as a primary cause of slip and melt fracture. The results demonstrate that methods to improve adhesion, by proper choice of materials of construction for the die land region and/or use of adhesion promoters in the resin, virtually eliminate the rate‐limiting effects of melt fracture in commercial blown film fabrication. The results highlight a deficiency of standard capillary rheometer methods to delineate the influence of materials of construction and/or adhesion promoters on observed melt fracture characteristics with molten polyethylenes.