(extracted from vixcontango.com)
The VXX buys VX2 futures (second month) and sells VX1 futures (front month) on a daily basis. The SVXY shorts VX2 futures and covers VX1 futures on a daily basis. The closer we are to VX1 expiration, the smaller the amount of VX1 futures and the larger the amount of VX2 futures that are traded. The amount is proportional to the time to expiration. The daily weights of the VIXY and SVXY are available for subscribers of this site on the front page.
Because of the heavy reliance on VX1 and VX2 futures inside the Volatility ETF/ETNs, Contango is a very imporant indicator for traders of VXX and SVXY
So long as the Contango is positive and high that results in automatic increase in the SVXY even if the SPX, spot VIX and VX futures are flat for the day. That same dynamic results in automatic decrease for the VXX. For example, if the Contango is 10%, that usually means the SVXY will increase 0.5% automatically provided there are no changes to the VIX. Why 0.5%? Because you divide the Contango by the amount of trading days during the VX1 contract term. Only that that portion of futures inside the ETF gets rolled over on a given trading day. Usually, VX future contract terms are either 20 or 25 trading days (4 weeks or 5 weeks). So you divide 10% by 20 to get to 0.5%.
If average contango is high, over time SVXY (Short Volatility ETF) can be expected to gain value above the average reduction in the spot VIX. This explains the SVXY outperformance over the S&P 500 index and it is important to understand that it is not an accident and it is not something that is propped up artificially high because "there a lot of buyers". The Volatility ETFs stick to their formula and if there is additional demand, they simply issue more shares. If there is less demand, they reduce the share count. But the share price of the ETFs follows the mathematical formula, period. As such the SVXY gains value based on VIX Futures fair value math and contango. So long as spot VIX is low and contango high, there is no limit to how high SVXY can go. And vice versa, there is no limit to how low VXX can go.
VXX Warning
While VXX are advertised to the general public as "portfolio insurance" product, it is anything but. Due to contango, the VXX may not rise when the market falls down. If contango is high and the market is slowly grinding down, the VXX will lose money daily. More often than not, the VXX will contribute significant percentage losses to your portfolio. Unless you are a day trader with volatility expertise, you should avoid investing or trading in VXX or other long volatility products .
Contango alone, however, doesn’t tell the whole story with regards to the SVXY. If the market drops and the VIX Futures Curve gets reset higher, the Contango is of lower importance now as what was formerly shorted VX2 at 15 (for example) inside the SVXY, now has to be covered as VX1 at 17 for a loss. This is what causes the SVXY to post massive daily losses during one or two day sell-offs in the market and why if the entire futures curve moves higher, the SVXY can start to lose you money quick. That is why while the SVXY can be a very powerful passive investment instrument, it still needs to be monitored constantly in order to avoid the large percentage drawdowns that inevitably come about (see performance of SVXY in the back half of 2014).