Proposal of Novel Evaluation Method for Moisture Transfer Properties of Waterproof Sheets for Nursing Care

Waterproof sheets for nursing care are designed to protect bedding during urinary incontinence, and their consumption has increased in recent years. Considering data related to heat and moisture transfer properties for commercially available waterproof sheets, we proposed objective indices for evaluating moisture transfer characteristics based on humidity changes over time obtained with a simulated skin device, and their usefulness was examined. Experiments were conducted under controlled conditions at 20°C and 65% RH, using 16 types of commercially available waterproof sheets and two types of cotton sheets as controls. Physical characteristics, as well as heat and moisture transfer properties of each sample―including contact cooling/warming sensation, moisture permeability, and water absorbability―were measured. In wetting simulations with a simulated skin device, water was discharged for 2 min so that the entire surface of the simulated skin became wet, and the temporal changes of temperature and humidity inside the sheets were recorded for 3 h. Heat transfer properties were evaluated using thermal resistance and evaporative heat resistance. Moisture transfer properties were assessed through three novel indices derived from temporal humidity changes within the sheet: the rate of humidity rise, the duration of high humidity, and the rate of humidity change. No inconsistencies were observed between these indices and the measured properties of the sheets. The use of these indices enables evaluations of the microclimate inside waterproof sheets, perceived wetness, and risks of pressure ulcers when sheet users experience urinary incontinence. From the perspective of improving users’ quality of life, these indices are considered useful for assessing product performance. This study suggests that optimal waterproof sheets should exhibit low evaporative heat resistance, a low rate of humidity rise, a short duration of high humidity, and a low rate of humidity change, demonstrating the possibility of objective evaluations of product quality.