Hartley’s rule

Hartley’s rule states that for a protein or polymer to be stable and function properly, its core region—or hydrophobic interior—should be about 20-25% of the total surface area. This balance ensures the molecule is sufficiently packed internally to maintain its structure while keeping enough surface exposed to interact with the environment or other molecules. In simpler terms, the rule helps predict when a protein’s shape is just right for stability and activity, based on the proportion of its hidden, water-repelling parts relative to its overall size.