Significance We provide insights into the sequence–conformation–property relationship that is central to the mechanical properties of protein elastomers. We find that a high content of glycine residue alone, not including proline, is sufficient for achieving near-perfect resilience. The content of proline residue may be associated with the metastability of random coils. Also, Raman spectroscopy, as a potent tool for investigating the conformation–property relationship, gives rise to a direct correlation between semiquantitative Raman features and the magnitude of elastic resilience. Moreover, metastable conformation or conformational polymorphism is useful to develop continuously and mechanically graded protein materials that may exhibit unique structural merits. This work underlies the exploitation of natural and de novo–designed sequences for protein elastomers and materials.