The exchange traded fund industry continues to expand its product line, providing investors with a growing number of strategies to customize and maximize their portfolios.

According to XTF data, there are now 1,843 exchange traded products, which include exchange traded funds and exchange traded notes, with $2.15 trillion in assets under management. Fund sponsors launched 280 new products this year but delisted 99.

Among the most popular new ETFs of 2015, the SPDR DoubleLine Total Return Tactical ETF (NYSEArca: TOTL) has accumulated $1.76 billion in assets under management after launching on February 23, 2015. TOTL, an actively managed ETF backed by bond guru Jeff Gundlach, is seen as an ETF adaptation of the DoubleLine Total Return Fund (DLTNX). More fixed-income investors may have shifted into an active bond ETF in hopes that an engaging fund manager would be more adept at adapting to changes in the markets, especially during a rising rate environment. [Smoking Gundlach: Why This Year’s Hottest New ETF Continues To Grow]

The second most popular ETF of the year is the SPDR S&P North American Natural Resources ETF (NYSEArca: NANR), which has quickly attracted $697.0 million in assets after only launching on December 15, 2015. NANR tracks the S&P BMI North American Natural Resources Index and holds large positions in some of the most downtrodden U.S. sectors, including 52.0% materials and 43.0% energy, which suggests that some large players could be using the new ETF to bet on a turn in the commodities producer space. [A New Way of Looking at Natural Resources]

The iShares Exponential Technologies ETF (NYSEArca: XT) has attracted $647.5 million after its launch on March 19, 2015. XT follows a group of developed and emerging market companies that are engaged in so-called exponential technologies. Specifically, these companies included innovative leaders that will transform the technology space or firms that develop or leverage promising technologies. Along with a hefty 32.5% tilt toward the information technology sector, XT includes a 30.5% position in health care, 11.5% in industrials, 11.2% in telecom and 4.4% in consumer discretionary. The underlying portfolio is also equally weighted so smaller companies have a larger impact on the fund’s performance. [Second Place Isn’t Bad For This ETF]

The Goldman Sachs ActiveBeta Emerging Markets Equity ETF (NYSEarca: GEM), which launched on September 25, 2015, has already attracted $572.8 million in assets under management. According to Goldman Sachs, GEM experienced a major growth spurt this month due to large institutional investor interest. The sudden interest in the Goldman Sachs ActiveBeta Emerging Markets Equity ETF may have to do with the end of the year. While we can only speculate, the timing of the increased inflows suggests that some institutional investors may be implementing a tax-loss harvesting strategy with an emerging market ETF to maximize their portfolios. On the other hand, some may just be enticed by GEM’s smart-beta indexing methodology, which targets companies with good value, strong momentum, high quality and low volatility. [A Fast Growing Smart-Beta Emerging Market ETF]

The SPDR Russell 1000 Low Volatility Focus ETF (NYSEArca: ONEV) has also quickly gathered $335.9 million in assets after launching on December 2, 2015. ONEV was developed with Alaska Permanent Fund Corporation (APFC), which infused the ETF with about $333 million, along with two other new smart-beta Russell 1000 ETFs. The Russell 1000 Low Volatility Focus ETF targets large-cap companies that exhibit small swings or low volatility. The top sector picks include financials 20.1%, consumer discretionary 16.4% and producer durables 15.7%.

For more information on ETFs, visit our ETF performance reports category.

Max Chen contributed to this article.