 At temperatures or denaturant concentrations close to their apparent midpoints, proteins may switch from downhill to two-state folding, the "type 0" to "type 1" transition.Global downhill folding (or "one-state folding") is another scenario in which the protein folds in the absence of a free energy barrier under all conditions.In other words, there is a unimodal population distribution at all temperatures and denaturant concentrations, suggesting a continuous unfolding transition in which different ensembles of structures populate at different conditions.