The insertion energy of charged residues is not additive. Peptides were constructed with the sequences listed above flanked by 12 glycine residues. A helix with a single arginine at the center of the membrane is 10 kcal/mol less stable than one with an alanine, but the addition of a second arginine makes the peptide only 1 kcal/mol less stable since the membrane has already bent to expose the central arginine. Further, the cost of including a third charged arginine is similarly an additional 1 kcal/mol. Helices with arginines spaced 2 apart (RXXR) are more stable than those with no spacing or single spacing since the membrane must only bend on one side of the helix to expose the residues to water. This incurs minimal elastic and nonpolar penalties. Helices indicated by * and ** were also created as 3₁₀ helices, and their energy values are discussed in the main text.