The ULTIMATE Growler - 2 Litre This growler is made from 304 grade stainless steel that is completely impervious to oxygen or sunlight (UV) meaning your precious amber liquid is in the absolute best storage container possible. Vacuum Wall Insulated Unlike other growlers this growler comes with double wall vacuum insulation to give you insulation like no other growler. So forget taking the esky, this baby will stay cold for hours. Sprung Wire Lid for Best Pressure Holding Capacity Most screw cap growlers struggle to hold the pressure required to keep beer fresh and carbonated. The ULTIMATE Growler comes with spring wire lid capable of holding up to 40psi.