Introduction: The special structure and use of underwear diapers make them have more complex heat and moisture transfer characteristics. The focus of comfort research is on heat transfer properties and their thermal and hygroscopic coupling with the human body and the environment.

1.Heat and moisture transfer within the fabric system

In the dry state, the heat transfer principle of panty-shape diaper is similar to that of general fabrics, but the heat transfer resistance is larger. The absorption of urine complicates the heat transfer process in the fabric system. Due to the changes in heat and moisture properties caused by material deformation, clothing volume, inter-fabric gaps, and microclimate temperature and humidity under the clothing, wearers often want it to have a lower heat retention rate to reduce sultry heat. After the fabric absorbs moisture, the thermal conductivity will change, especially after absorbing moisture, the thermal conductivity and maximum heat flux will increase, and the thermal insulation will decrease.

Compared with ordinary fabrics, the SAP particles in panty-shape diaper will inhibit the activity of water molecules when absorbing water. When the water reaches a certain amount, the SAP particles will expand rapidly, and the collision friction will release free water molecules again. Therefore, when the SAP particles absorbed the amount of urine excreted by an approximately one-year-old infant, their thermal conductivity increased rapidly, with a 2.5-fold increase in the maximum heat flux value and a 1.4-fold increase in thermal conductivity. This study helps to reveal the heat transfer mechanism and evaluate the performance of SAP particles in use.

2.Heat and moisture transfer in the microclimate

The heat and moisture transfer of the garment system plays a key role. panty-shape diaper has good sealing performance. Due to its blocking of the convection channel, the heat and moisture transfer in the micro environment under the clothes has a more obvious impact on the comfort of human clothing.

Factors such as structure, material, and wearer's state affect the characteristics of the microclimate, such as temperature and humidity. The underwear type panty-shape diaper is easier to dissipate heat and moisture than the open type, and it is also more suitable for bedridden patients or night use. By analyzing the relationship between its physical properties and the distribution of temperature and humidity in the microclimate, it is found that the moisture permeability, humidity drying rate and thermal and humidity comfort are significantly related.

At present, the evaluation of heat and humidity comfort has made some progress in monitoring the heat transfer characteristics and microclimate temperature and humidity change laws, the heat and humidity transfer laws between multi-layer structures are still unclear, and the dynamic heat and humidity transfer mathematical model has not been established. Thermal humidity comfort is significantly affected by the heat transfer ability and structure of the fabric, the superior wet and fast drying of the surface coating material can improve thermal humidity comfort, the thickness and its relatively closed skin space will have a negative impact on human thermal humidity comfort, so the thermal humidity comfort of underwear diapers and their own absorption and anti-side-leakage performance have certain contradictions, future research should pay attention to the balance of the two parts of the function, but also to continuously conduct surveys and statistics to collect user feedback to improve the overall use performance.