We examined and compared low-stress mechanical properties, such as tensile, shear, bending, compression, and surface properties, measured by the Kawabata Evaluation System for Fabrics (KES-FB), of polyethylene terephthalate (PET) and poly(lactic acid) (PLA) fabrics before and after softening with commercial softeners. The bending and shear properties of both fabrics were influenced by the chemical nature of the softening agents and the emulsion type used in the softener. In contrast, the ionicity and hydrophobicity of the softener appeared to have little or no effect on bending and shear properties of both fabrics. There is no clear trend showing that the LT, RT, MMD, MIU, LC, and RC values of both fabrics were influenced by any of the following properties of the softeners: the chemical nature, emulsion type, ionicity, or hydrophobicity. The best performing softener for both fabrics was a slightly cationic hydrophobic amino-functional poly-dimethyl-siloxane micro-emulsion softener. Overall, all softened PLA fabrics exhibited lower bending rigidity, tensile linearity, and tensile resilience as well as higher tensile energy, extensibility, geometrical roughness, mean deviation of friction, and compression energy values than all softened PET fabrics, leading to a softer, fuller, and fluffier but rougher fabric handle.