ProShares UltraShort S&P 500 tries to provide twice the inverse, or opposite, return of the S&P 500 on a daily basis.

“Leveraged funds are expensive and extremely risky, so they are best left to speculative traders or hedgers who have the desire to monitor and trade their positions daily,” wrote Morningstar analyst Michael Rawson in a profile of the ETF. “The mathematics of compound interest make volatility a hidden cost to this fund.” [How Volatile Markets Impact Leveraged ETFs]

Leveraged and inverse ETFs are sharp tools, so investors need to be careful. As always, it’s important for investors to know exactly what their ETF holds and how the strategy works. [Know Your ETF’s Holdings]

Despite recent negative headlines, leveraged ETFs captured 15% of the industry’s inflows in the third quarter. [Bond, Leveraged ETFs See Big Inflows]

Some of the other largest exchange traded products that short U.S. stocks include Direxion Financial Bear 3X Shares (NYSEArca: FAZ), ProShares UltraShort QQQ (NYSEArca: QID) and Direxion Small Cap Bear 3X Shares (NYSEArca: TZA).