Note 6. Patents and Other Assets

Patents represent legal fees and filing costs that are capitalized and amortized over their estimated useful lives of 17 to 20 years or their remaining legal lives, whichever is shorter, after they are placed in service. There were no patents placed in service for the years ended December 31, 2014 and 2013. In both 2014 and 2013, we capitalized approximately $0.1 million for patent filing costs, for a total investment in patents of approximately $0.8 million and $0.7 million as of December 31, 2014 and 2013, respectively.

No amortization expense of patents was recorded in either of the years ended December 31, 2014 and 2013. These patents were not placed in service for the years ended December 31, 2014 and 2013, or in prior years.