Diaper testing poses unique testing challenges including a multi-layered composited structure and evaluation of a closed microclimate system. This work evaluated the microclimate of daytime and nighttime diapers, with and without a garment assembly. Results indicated that the addition of a garment further affected temperature and humidity and restricted water vapour transmission, although the nighttime garment had a greater impact on the microclimate. The study also explored the relationship between thermal comfort and microclimate conditions. A significant increase in time spent in the thermal comfortable zone was found in the daytime diaper and garment system compared to diaper only. In comparison, the nighttime diaper only and diaper garment system spent more time in the thermal discomfort zone. In sum, parents need to try to find a balance between the insulation level of garments donned over the diaper and the thickness of the diaper itself. [ABSTRACT FROM AUTHOR]