Exchange-traded funds, like their traditional mutual fund cousins, were originally targeted at mainstream investors as an easy way to get exposure to segments of the stock and bond markets. Now large investors, such as pension funds and sovereign wealth funds, are increasingly turning to ETFs to help manage their liquidity concerns.

Institutional investors made up 21.2 percent of assets in ETFs last year, up from 18.9 percent in 2015, according to a report today from Greenwich Associates, which interviewed 187 such investors for its 2016 U.S. Exchange Traded Funds Study.

Institutions are adding ETFs to their portfolios for traditional investment reasons, but they’re also adding the funds to help manage risks and liquidity, according to Andrew McCollum, a Greenwich consultant. For example, they’re adding indexed high-yield bond ETFs as an alternative to buying individual securities in the bond markets, which can become less liquid, or more difficult to trade. Half of institutions use ETFs for liquidity and risk reasons.

BlackRock’s iShares ETF product line was the top choice for institutions based on such factors as liquidity, trading volume, expenses and performance. Ninety-nine percent of those surveyed by Greenwich use iShares; 68 percent use State Street Global Advisors’ SPDR lineup; two-thirds use ETFs from Vanguard Group and 48 percent use PowerShares.

The survey also found that institutional investors plan to increase their use of ETFs this year. Forty seven percent of investors in equity ETFs say they will increase their holdings, compared to 38 percent of bond ETFs users. Still, bond ETFs are gaining in popularity, with assets in bond ETFs rising 26 percent to $428 billion last year, outpacing an 18 percent increase for equity ETFs.

Smart beta ETFs are also on the rise. Greenwich found that smart beta made up 37 percent of institutions’ ETF use in 2016, up from 31 percent in 2015. These ETFs are alternatives to market-cap weighted index funds, such as those that track the Standard & Poor’s 500.

Another big source of demand for ETFs is coming from managers of multi-asset funds, which pull a broad array of investments into a diversified portfolio designed around a specific objective such as low volatility. Greenwich reports that 52 percent of asset managers used ETFs for this reason in 2016, up from 35 percent the year before. The proportion of multi-asset funds that are made up of ETFs is also growing. A U.S. manager of a multi-asset portfolio, who declined to be named, told Greenwich, “ETFs have increased over the past 10 years from 50% to 90% of our strategy.”