Criterion for Quantifying Skin Mechanical Stimuli during Tactile Assessment of Ultra-Soft Materials such as Towels

The tactile sensation of towel fabrics, which originates from their pile structure, is strongly affected by the mechanical response under the low loads applied at the instant of contact. The pile structures formed from spun yarns create a graded surface with extremely low elasticity at the outermost layer, complicating the quantitative assessment of tactile properties. This study proposed a quantitative framework for evaluating the tactile performance of ultra-soft textiles using low-load indentation testing and finite element analysis (FEA). Mechanical responses of towel samples were measured through controlled indentation and incorporated into an FEA model simulating skin contact. Stress-based indices-including pressure, principal stresses, Tresca stress, and von Mises stress-were calculated to characterize mechanical stimuli applied to the skin. Correlations between these indices and the initial elastic modulus of the pile structure were examined to identify parameters reliably representing tactile performance. The results show that Tresca and von Mises stresses exhibit strong linear relationships with the structural modulus even under low-stress conditions, highlighting their potential as objective design metrics for developing textiles with targeted tactile qualities. This framework provides a systematic approach for quantitatively linking fabric microstructure to perceived tactile behavior, facilitating design optimization of ultra-soft materials.