While U.S. benchmarks retreated Friday and were on course for their worst weekly performance in a month, the CBOE Volatility Index and VIX-related exchange traded funds surged on the elevated risk-off sentiment.

Exchange traded products that try to track the VIX were among the best performers on Friday as major stock indices declined over 1.5%. For instance, the iPath S&P 500 VIX Short Term Futures ETN (NYSEArca: VXX) rose 11.4%, ProShares VIX Short-Term Futures ETF (NYSEArca: VIXY) gained 1.4%, AccuShares Spot CBOE VIX Up Shares (NasdaqGM: VXUP) advanced 13.6% and C-Tracks on Citi Volatility Index ETN (NYSEArca: CVOL) increased 14.6%.

Meanwhile, the CBOE Volatility Index jumped 26.8% to 24.5 – the so-called fear gauge has historically traded between the 15 to 20 range. The VIX reflects the market’s expected 30-day volatility, so a rising VIX indicates investors’ concerns over the equities market.

Investors should keep in mind that the majority of VIX ETPs are designed to track CBOE Volatility Index futures contracts, not the VIX spot price. It’s a very important difference.

The equities market was lower Friday amid concerns that the continued weakness in the Chinese yuan currency could weigh on the global economy and on industries that export to China, reports Tanya Agrawal for Reuters.

U.S. stocks were also dragged lower after crude oil prices dipped below their seven-year lows.