An experimental study of friction between volar forearm skin and nonwoven fabrics used in disposable absorbent products for incontinence.

Incontinence-associated dermatitis is common among wearers of absorbent incontinence products and friction between product materials and skin is thought to be a contributing factor, but the details of its role are unclear. In this study, friction was measured between the dry volar forearm of 19 women (20-95 years) and five nonwovens typical of those in commercial disposable products. Euler's model/Amontons' law held to high precision for all person-fabric pairs for both static and dynamic friction, despite substantial variations in forearm size, soft tissue compliance and skin smoothness between subjects, sometimes substantial lateral contraction in fabric strips, and skin rucking beneath them. For a given subject, the highest coefficients of friction among the fabrics exceeded the lowest by ∼30% to 75%, while - for a given fabric - the highest coefficients of friction among the subjects exceeded the lowest by ∼55% to 85%. The order of coefficient of friction values across fabrics was similar for each subject, and across subjects for each fabric. There was no systematic variation with subject age. The data were well modelled by estimating the coefficients of friction for a given person-fabric combination as the product of the mean coefficient of friction across all fabrics for that person, and the mean coefficient of friction across all persons for that fabric, normalised to the mean coefficient of friction across all person-fabric combinations. Predicted values were within 10% of measured figures for ∼97% of person-fabric combinations. Stick-and-slip behaviour was observed with seven person-fabric combinations, but especially strongly for two subjects with each of two fabrics. It is not clear why and further investigation is merited. Comparison of the data with results from earlier work with the same fabrics and a skin surrogate (Lorica Soft) suggests that measurements with Lorica Soft may be helpful to screen, evaluate and compare candidate materials preparatory to human studies.