(Bloomberg) -- Investors are taking their fascination with low-volatility stocks to new heights.

The PowerShares S&P 500 Low Volatility fund and the iShares Edge MSCI Minimum Volatility USA ETF saw combined assets reach $20 billion this month for the first time, adding $7 billion for the year, exceeding the total for 2014 and 2015 combined. Due mostly to inflows, the market value of the PowerShares ETF jumped by about $1.3 billion this year, while the iShares fund has seen its capitalization roughly double to $13.1 billion.

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