NEW YORK ( TheStreet ) — An important point I’ve made repeatedly over the years has been the need to look under the hood of any exchange-traded fund to understand the index constituency before buying. A great example of this is the myriad of infrastructure ETFs that have been issued in the last few years.

There are more than half a dozen infrastructure funds and despite targeting the same theme and having the word infrastructure in their names they are quite different. Thinking one fund is better is probably the wrong way to look at it given the divergent approach they take to accessing the theme. Each fund has its own attributes and so the right fund for you may not be the right fund for someone else.

From the top down, the theme is compelling because we know the money is going to be spent — over $1 trillion just in India from 2012 to 2017. It must be spent and there is no doubt it will happen. This creates a tailwind for any related companies. The risks include normal market volatility, inefficient spending decisions and corruption on the ground where projects are undertaken.

The first fund in this space was the SPDR FTSE/Macquarie Global Infrastructure 100 ETF (GII ). What makes this fund unique to the group is its enormous 85% weight to utilities. As a result, the fund has generally been less volatile than the broad market and the other infrastructure funds. While it is a positive that the fund went down less than the market during the panic, it also has gone up much less than the market and most of the other funds in the category during the rally that started almost two years ago. Like utility stocks or funds, one of the big risks here will be rising interest rates. Utilities tend to get hurt when rates rise as money rotates from the stocks to bonds looking for yield without equity risk.

At the extreme other end of the spectrum is the PowerShares Emerging Markets Infrastructure Portfolio (PXR ). This fund is heaviest in industrial stocks at 56%, which makes sense, but it also allocates 40% to materials stocks which when combined with being an emerging-market fund creates a lot of volatility. This fund didn’t come along until late 2008 so it missed a large portion of the market panic. But anyone in this fund should expect larger declines when the market goes down a lot and larger gains when the market rallies. From the March 2009 low. this fund is up 183% vs. 75% for the S&P 500 and 26% for the previously mentioned SPDR Infrastructure fund. Again, this does not make the PowerShares fund better or worse but illustrates the extent to which this is a completely different exposure to the theme. Looking ahead, this fund will get hit very hard if the market goes down a lot or if commodity prices have a meaningful correction.