February marked the 49th consecutive month of net inflows to exchange-traded funds (ETFs), and by the end of the month, ETFs listed around the world had $4.968 trillion in combined assets under management, according to ETF research firm ETFGI.

Still, the percentage of investors owning ETFs implies that there is plenty of room for growth in the industry. "Today, one in three U.S. investors owns an ETF, according to BlackRock's latest ETF Pulse Survey," said BlackRock, Inc. (BLK). "That's up from one in four last year, but we are just getting started. By 2020, we expect half of such investors to be following your lead and making ETFs an integral part of how they build portfolios." (See also: A Brief History of Exchange-Traded Funds.)

BlackRock is the world's largest asset manager and the parent company of iShares, the world's largest ETF sponsor. The firm compares ETFs to a disruptive, transformative technology – a comparison that has been made many times over the years as ETFs have altered the investment universe. "Another transformative technology is catalyzing change," said BlackRock Managing Director Martin Small in an open letter to investors. "More and more people are choosing ETFs to actively pursue the goals that matter most to them, by tapping into markets and strategies that were once available to only the most deep-pocketed professionals."

Across generations, ETF usage varies. Forty-two percent of millennial investors are using ETFs, but just 27% of baby boomers are embracing this asset class, according to BlackRock. In fact, ETF usage among baby boomers trails that of Gen X and the silver generation (those ages 70 and up). (For more, see: Boomers Lag Gen X, Millennials When It Comes to ETFs.)

Among the top 10 reasons to choose ETFs cited by investors in the BlackRock survey, three are cost related. Of ETF users surveyed, 41% said they like the low fees associated with the products, while 38% said the low costs to transact in ETFs are attractive. Related to that second point, 24% of investors say they like commission-free ETF platforms, according to BlackRock.

Various data points have long reflected investors' preference for low-fee funds. Over the past several years, a significant percentage of ETF inflows have been directed to those products with annual expense ratios of 0.20% or less. Of 2017's top 10 asset-gathering ETFs, only the iShares MSCI EAFE ETF (EFA) had an annual fee north of 0.20%. Year to date, the iShares Core MSCI EAFE ETF (IEFA), which is the low-fee alternative to EFA, and the iShares Core S&P 500 ETF (IVV) have added over $25.7 billion in new assets combined. IEFA and IVV have annual fees of just 0.08% and 0.04%. (For additional reading, check out: Minimizing ETF Fees.)