Although higher beta momentum strategies and stocks have been performing well this year, some low volatility exchange-traded funds are at least keeping pace with the S&P 500. For example, the  iShares Edge MSCI Min Vol USA ETF (NYSE:USMV) and the PowerShares S&P 500 Low Volatility Portfolio (NYSE:SPLV) are up an average of 11.8 percent year to date.

USMV and SPLV are the two largest low volatility ETFs trading on U.S. exchanges, but as has been noted over the years, there are significant differences between the two kings of the low volatility ETF space.

“USMV is the largest of the low/minimum volatility ETFs with $14 billion in assets,” said CFRA Research Director of ETF & Mutual Fund Research Todd Rosenbluth in a note Monday. “USMV tracks an optimized index aiming to generate the lowest absolute volatility with sector constraints of 500 basis points relative to its parent MSCI USA index. USMV is reconstituted on a semi-annual basis, most recently in May, to reflect shifting market movements.”

Related Link: Don't Forget This Europe ETF

Looking Inside

USMV follows the MSCI USA Minimum Volatility (USD) Index and holds 190 stocks. The ETF allocates over 38 percent of its combined weight to the healthcare and technology sectors. USMV's nearly 19 percent weight to the technology sector is perhaps surprising and undoubtedly large among low volatility strategies.

The rival SPLV has also been increasing its technology exposure to the point that the ETF's weight to that sector is currently the highest it has been in over six years on the market.

SPLV tracks an index that has no sector constraints and focuses on just stocks with the lowest 12-month volatility. SPLV is reconstituted on a quarterly basis, most recently in late August, said Rosenbluth. “Financials (21 percent of assets), industrials (18 percent) and utilities (17 percent) were the largest sectors at the end of August, while exposure to technology (11 percent) and health care (5 percent) was much lighter than at peer USMV.”

PLV tracks the S&P 500 Low Volatility Index, which is home to the 100 S&P 500 members that have the lowest trailing 12-month volatility.

“Since inception in 2011, the S&P 500 Low Volatility Index exhibited a down-capture of 43% and actually rose in one of the 10 worst markets since 2011,” according to PowerShares.

SPLV also has mid- and small-cap equivalents that follow low volatility answers to the S&P MidCap 400 Index and the S&P SmallCap 600 Index.

Related Link: An Anti-Dollar Play