Measurement of tissue paper softness: A literature review

Along with strength and absorbency, softness is a key consumer attribute for tissue paper products. It has been of academic and commercial interest to develop physical test methods that can be related to softness. With a good physical relationship, small quantities of test materials can be evaluated, new products can be developed, and advertising and intellectual property claims can be made. This paper reviews the literature published on softness measurement methods, including panel tests and the attempts to relate the perceived softness to physical measurements. Most investigators measured individual bulk or surface properties and then used multiple regression analysis to determine correlations. The paper covers the literature that identifies the distinction between bulk softness and surface softness. Bulk property measures include; compression, tensile stiffness, elongation, bending stiffness, and sonic modulus. Surface property measures include texture and friction. Instruments have been developed to make combined measurements simultaneously, like bending and friction. To date no single instrument or physical method used alone has been found to adequately classify a broad range of samples in the same fashion as the human hand and brain. The use of multiple measures and physical tests is required. Developmental trends in the field of remote sensing and surgery may lead to new insights and instrumentation that could eventually tell us how the human hand senses touch. This could then lead to the development of the single instrument softness machine.