In another study, Rollins and Dill (2014) introduces the Foldon Funnel Model, a new addition to previous folding funnels, in which secondary structures form sequentially along the folding pathway and are stabilized by tertiary interactions. The model predicts that the free energy landscape has a volcano shape instead of a simple funnel that is mentioned previously, in which the outer landscape is sloped uphill because protein secondary structures are unstable. These secondary structures are then stabilized by tertiary interactions, which, despite their increasingly native-like structures, are also increasing in free energy until the second-to-last to the last step that is downhill in free energy. The highest free energy on the volcano landscape is at the step with structure just before the native state. This prediction of energy landscape is consistent with experiments showing that most protein secondary structures are unstable on their own and with measured protein equilibrium cooperativities. Thus, all earlier steps before reaching the native state are in pre-equilibrium. Despite its model being different from other models before, the Foldon Funnel Model still divides conformational space into the two kinetic states: native versus all others.