IMB approved to become a mutual bank 24 June 2015 3:50PM John Kavanagh The Australian Prudential Regulation Authority has approved IMB's application to become a mutual bank. IMB announced yesterday that it would begin trading under the name IMB Bank on August 1.IMB, which has around 180,000 members and A$5 billion of assets, said it would not change its ownership structure or business model.IMB chairman Michael Cole said in a statement that the change would help the institution market to young people, who don't know what a building society does.Credit unions and building societies have been able to convert to mutual banks since 2011. Most of those that have done so report positive results, with a wider range of customers prepared to bank with them.