| Hydropathy characteristic | Abbreviation | Amino acids |
| Strongly hydrophilic (polar) | POL | R, D, E, N, Q, K, H |
| Strongly hydrophobic | HPO | L, I, V, A, M, F |
| Weakly hydrophilic or weakly hydrophobic (ambiguous) | AMBI | S, T, Y, W |
| Undefined | UND | C, G, P |