Financial professionals should do better at explaining the benefits of exchange-traded funds to clients and why they work well in most investment and retirement plans.

Those were the contentions of BlackRock U.S. Wealth Advisory officials at a news conference in Manhattan on Tuesday. They noted an irony: Investors are pouring money into ETFs at an explosive pace that will continue over the next few years, yet many other investors won’t touch them.

Black Rock officials said only one in five retail investors are using these relatively new funds. They said over the last 20 years, ETF investments have grown from zero to $3 trillion, with some $1.3 trillion in domestic retail ETFs. They predicted ETF assets will grow to just under $4 trillion over the next two years. BlackRock has about $850 billion of those ETF assets, held by advisors and do-it-yourself investors.

“The defining issue is going to be retirement,” says Heather Pelant, head of personal investing for BlackRock’s U.S. Wealth Advisory.

With the decline of defined benefit plans, many investors near or in retirement must make their own retirement-planning decisions. The numbers of people needing to plan and control investments for retirement will continue to increase. “Within five years, retirees or pre-retirees will control 70 percent of the wealth assets,” Pelant said.

Over the last year, ETF assets have jumped 14 percent, says BlackRock. “And we think that organic growth is going to continue as an industry for at least over the next three to four years,” according to Mark Wiedman, global head of iShares at Black Rock.

This comes at the same time that flows into actively managed equity mutual funds are slowing down, according to Frank Porcelli, head of BlackRock’s Advisory Group. He  also said that most actively managed funds are not beating indexes, which he believes makes the case for indexing and ETFs.

But, despite the popularity of ETFs with some, why are 80 percent of U.S. retail investors not using them? “I find that actually somewhat shocking because they should be the foundational element of every retail investor’s portfolio,” Wiedman added.

But many individual investors still don’t understand the product, the cost advantages or how ETFs can be used to shape an investment portfolio, BlackRock officials said. ETF fees are about one-third of what the average mutual fund charges, and ETFs incur about 50 percent less in taxes, BlackRock officials said, citing cited Morningstar figures.

The problem with trying to persuade people to use ETFs, Wiedman added, is the term. ETF, he added, “is actually a bit of a turnoff and actually alienating.” Wiedman noted that even some of his relatives don’t understand what an ETF is.

Wiedman also called for advisors and other financial professionals to demystify this product. He said the simplest way to explain the ETF is “a fund that trades like a stock. It is a low-cost, efficient investment vehicle.”

Advisors and others should understand that investors are comfortable with other investments, which is why the ETF market is still relatively small compared to traditional mutual funds, Wiedman said.

“People feel all warm and fuzzy in a mutual fund as a structure. It sounds safe and comfortable. Changing the behaviors of people to buy something that is a more efficient way to invest is a long-term journey,” he said.

Wiedman pointed to pension plans. Only three years ago, he said, they started using ETFs on a big scale, even though the product has been around for some 20 years.