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The inclusion of peptoid monomers into antimicrobial peptides (AMPs) increases their proteolytic resistance, but introduces conformational flexibility (reduced hydrogen bonding ability and cis/trans isomerism). We here use NMR spectroscopy to answer how the insertion of a peptoid monomer influences the structure of a regular α‐helical AMP upon interaction with a dodecyl phosphocholine (DPC) micelle. Insertion of [(2‐methylpropyl)amino]acetic acid in maculatin‐G15 shows that the structural change and conformational flexibility depends on the site of insertion. This is governed by the micelle interaction of the amphipathic helices flanking the peptoid monomer and the side chain properties of the peptoid and its preceding residue.A high‐resolution structure of a peptoid–peptide hybrid (“peptomer”) is presented. The peptoid residue breaks the helix and displays cis/trans isomerism. Maculatin‐Nleu11 displays only the trans isomer. Maculatin‐Nleu13 displays almost equimolar amounts of cis and trans conformers. Peptide amphipathicity and peptoid hydrophobicity govern the cis/trans isomerism. [ABSTRACT FROM AUTHOR]