What is the mix of optimal capital structure?

There is nothing called optimal capital structure. optimal capital structure for a company refers to the composition of debt and equity, where the firm cost of capital is the lowest and value of the firm the highest. Optima capital structure for one company can not be same for the other company as well as the firms differ from each other in their basic characteristics. Even if the firm have same basic characteristics, they differ in Human resource, skill set etc.