||PURPOSE: To evaluate the effect of 7 viscoelastic materials on the physical properties of the Unfolder lens injection system. SETTING: John A. Moran Eye Center, University of Utah School of Medicine, Salt Lake City, Utah, USA. METHODS: New sterile SI-40NB intraocular lenses (IOLs) were loaded into the Unfolder (AMO PhacoFlex II SofTip insertion system (Allergan) using 7 viscoelastic materials: sodium hyaluronate 1.0% (Healon, Provisc), sodium hyaluronate 1.4% (Healon GV), sodium hyaluronate 1.6% (Amvisc Plus), hydroxypropyl methylcellulose 2.0% (Occucoat), sodium chondroitin 4.0%--sodium hyaluronate 3.0% (Viscoat), and hyaluronate 3.0% (Vitrax). The IOLs were then injected after 10 or 120 seconds in the chamber (chamber dwell time) and 10, 60, or 180 seconds in the barrel of the Unfolder cartridge (barrel dwell time). Torque values (g/cm) required to extrude the lenses were measured with a torque gauge, and the cartridges and IOLs were inspected for damage. RESULTS: Longer chamber dwell times resulted in lower torque values to extrude the IOLs (P < .001). Conversely, longer barrel dwell times resulted in higher torque requirements for IOL extrusion (P < .001). Furthermore, rates of adverse events, such as nondelivery, IOL damage, or Unfolder cartridge damage, were higher with shorter chamber dwell times and longer barrel dwell times (P < .001). However, IOL damage was avoided when the manufacturer's recommended chamber and barrel times were used. CONCLUSION: Increasing chamber dwell time and decreasing barrel dwell time resulted in lower torque values to extrude IOLs from the Unfolder and increased successful use. Moreover, dispersive viscoelastic agents tended to be more forgiving of changing dwell times and therefore had lower torque values and adverse event rates overall.