With U.S. stocks continuing to soar and interest rates remaining low, encouraging investors to flock to longer-dated Treasury exchange traded funds, 2014 has been another year to remember for the ETF industry.

Through the first 11 months of the year, U.S. ETFs have added $192 billion in new assets, a total that already tops the inflows record set last year. Now, it is just a matter of days before the U.S. exchange traded products tops $2 trillion in assets under management.

With 2014 drawing to a close, those superlatives are about to be put in the rearview mirror, indicating it is time for investors to start considering what could be prominent ETF themes and trends in 2015.

“We believe heading into 2015, when returns might be choppier, investors should consider low or minimum volatility products such as iShares MSCI USA Minimum Volatility ETF (NYSEArca: USMV) and the PowerShares S&P 500 Low Volatility Portfolio (NYSEArca: SPLV),” said S&P Capital IQ in a new research note.

SPLV, the largest low volatility equity ETF, and USMV have each bested the S&P 500 this year as some investors have opted to play a rally in U.S. stocks that has stretched over five years in conservative fashion. [Investors Favoring Low Vol ETFs]

SPLV and USMV are up an average of 14% this year and they have an average beta against the S&P 500 of 0.69. S&P Capital IQ rates both ETFs overweight.

“While these alternatively-weighted ETFs are constructed differently, from a security and sector perspective, we think they can each reduce an investors’ risk profile while allowing them to stay in the market. Both  hold stocks with above-average S&P Capital IQ Quality Rankings and generally low Qualitative Risk Assessments, according to our research supporting our top ranking,” said S&P Capital IQ.

The low volatility approach has worked with mid- and small-caps as well as highlighted by the PowerShares S&P SmallCap Low Volatility Portfolio (NYSEArca: XSLV) and the PowerShares S&P MidCap Low Volatility ETF’s (NYSEArca: XMLV). Though smaller than SPLV, XMLV and XSLV have each easily outpaced standard mid- and small-cap benchmarks, such as the S&P MidCap 400 and Russell 2000, this year. [Low Vol Works With Mid-Cap ETFs]

Another ETF theme expected to be prominent next year is investors trying to figure when the Federal Reserve raises interest rates, if that happens at all. That could be followed by inflows to short-dated bond ETFs.

“Within fixed income, we think investors will attempt to determine if, and when, the Federal Reserve will raise interest rates and what impact that has on their portfolios. While short-term ETFs were not very popular in 2014, as yields moved lower and investors were rewarded for taking on duration risk, we expect products such Vanguard Short-Term Corporate Bond ETF (NasdaqGM: VCSH) and the SPDR Short-Term High Yield ETF (NYSEArca: SJNK),” said S&P Capital IQ.