Natural gas prices are on the rise again after hitting a record low early last month. The onset of this month's cold snap may not please consumers, but it is warming investors.

Those who used an exchange-traded product to gain a long exposure two weeks ago will have bought in when futures prices were still around $3.32MMBtu, or one million British Thermal Units, and would have gained almost 4% had they sold at last week's price of around $3.44MMBtu.