IFM Investors chief executive Brett Himbury says the chief investment officers of the country's superannuation funds have increased their appetite for unlisted assets as a way to overcome the most "difficult investing environment" in three decades.

"There is a global trend in an environment of interest rates moving up, geopolitical confusion, changing macro economic and fiscal policies around the world where there is an increased appetite for unlisted assets," he said after the release of the asset manager's results for 2017-18.