Rotomoulded articles and methods of forming the same are described herein. The rotomoulded articles generally have a permeability of less than 1 g/day. The rotomoulded articles generally include polyethylene obtained by injecting into a reactor a catalyst system including a metallocene catalyst component of specific formula and an activating agent; injecting into the reactor ethylene monomer at a concentration of at least 6.5 wt %; injecting an amount of hydrogen such that a ratio of hydrogen to ethylene (H2/C2) in the feed is less than 85 g/106 g; maintaining the reactor under polymerisation conditions at a temperature of less than 90° C.; and retrieving polyethylene exhibiting a melt index (MI2) of at least 3.