When this happens, volatility ETFs lose money on the “roll trade” because they need to sell expiring VIX contracts and buy new ones.

The number of VIX futures contracts outstanding has more than tripled this year as investors hedge to protect stock gains, Bloomberg reports.

“Volatility has become more attractive now as an asset class,” said Nikolaos Panigirtzoglou, JPMorgan Chase & Co.’s European head of global asset allocation, in the story.

Shares outstanding in VXX have jumped almost nine-fold this year and hit a record earlier this month.

“It’s what I call a bull market in fear,” Christopher Cole, founder of Artemis Capital Management, told Bloomberg.

iPath S&P 500 VIX Short Term Futures ETN