The CBOE VIX Volatility Index is an interesting animal that has grown to become one of the most heavily watched indicators of fear and greed in the market. This index functions by measuring near-term volatility expectations from options activity on the S&P 500 Index (SPY). It’s calculated on an intra-day basis, so investors are able to watch as implied volatility expands or contracts in real time. The CBOE has a nice primer on how this is accomplished that you can read here.

As many ETF investors know, you can’t invest directly in an index. So the forward-thinking asset managers at Barclays, ProShares, and VelocityShares set out to create several products to help you invest in the movement of the VIX Index. According to data from ETF.com, there are currently 20 dedicated exchange-traded funds and exchange-traded notes that attempt to track this index with varying degrees of success.

The two largest funds in this space are the iPath S&P 500 VIX Short-Term Futures ETN (VXX) and VelocityShares Daily Inverse VIX Short Term ETN (XIV). Both of these funds currently have over $1 billion in assets under management. VXX is a bet on the expansion of volatility, which typically comes during a correction or choppy stock market action. Conversely, XIV is an inverse play that rises when volatility contracts. This fund is intended to move higher as stocks move higher and greed takes a more prominent position in investor sentiment.

There are also many other flavors of VIX funds that offer varying degrees of unique tracking and index construction methodology. Nevertheless, XIV and VXX work well as benchmarks to understand this unconventional asset class. I have been watching and even invested small amounts in these funds for my personal accounts at one point or another and these are the lessons I have learned from the experience.

1. They aren’t for the faint of heart. By their nature, VIX funds are a non-correlated index that is essentially a way to measure when the stock market starts to get shaky. It’s difficult to use these as a forecasting tool and they are often susceptible to VERY fast swings in price. They should truly only be used by disciplined traders, investment professionals, or those who understand their unconventional nature. In my opinion, they should only be held for very short periods of time with a tight stop loss to guard against significant downside risk.